Method and system for millimeter wave hotspot (mmH) backhaul and physical (PHY) layer transmissions

ABSTRACT

A method and apparatus are disclosed for communication in a Millimeter Wave Hotspot (mmH) backhaul system which uses mesh nodes. A mmH mesh node may receive a control signal which includes a total number of available control slots. The mesh node may determine the number of iterations of a resource scheduling mechanism that can be made during the time period of all available control slots, based on the number of neighbor nodes for the mesh node. Further, the mesh node may receive control slot information, including information about traffic queues and priorities. The mesh node may then perform resource scheduling using the resource scheduling mechanism based on the currently received control slot information and control slot information received in previous iterations of resource scheduling. The mesh node may also adjust a preamble based on a time between a last packet transmission and a current packet transmission to a neighboring node.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Stage, under 35 U.S.C. § 371, ofInternational Application No. PCT/US2014/060973 filed Oct. 16, 2014,which claims the benefit of U.S. Provisional Application No. 61/891,738filed Oct. 16, 2013, the contents of which are hereby incorporated byreference herein.

BACKGROUND

It is well known that the capacity demand in cellular networks has beengrowing exponentially for many years and is expected to continue thisway for at least the next decade. While advances in spectral efficiencywill continue, the gains that we can expect from these advances arelimited. Densification of cellular networks will continue to be theleading source of capacity gains until the use of higher frequenciesbecomes feasible for access link. Small-cells are currently being usedto increase the density of networks and address these capacity problems.This increase in cell density, however, requires a correspondingincrease in backhaul cap abilities.

Rolling out fiber to all of these new nodes is cost prohibitive. TheMillimeter Wave Hotspot (mmH) project proposes the use of highlydirectional millimeter (mm) wave links between these small-cell nodes asa way to address this concern. Small cells are expected to be rolled outfirst in dense urban environments of varying landscapes.

SUMMARY

A method and apparatus are disclosed for communication in a MillimeterWave Hotspot (mmH) backhaul system which uses mesh nodes. A mmH meshnode may receive a control signal which includes a total number ofavailable control slots. The mesh node may determine the number ofiterations of a resource scheduling mechanism that can be made duringthe time period of all available control slots, signaled by the controlsignal, based on the number of neighbor nodes for the mesh node.Further, the mesh node may receive control slot information fromneighbor nodes, wherein the control slot information includesinformation about traffic queues and priorities. The mesh node may thenperform resource scheduling using the resource scheduling mechanismbased on the currently received control slot information and controlslot information received in previous iterations of resource scheduling.In an example, the control signal may be received from a meshcontroller.

The resource scheduling mechanism may include a resource assignmentalgorithm. Further, the resource requests and temporary schedules forall priorities may be received in each iteration. Also, the number ofcontrol slot may vary based on the neighboring nodes. In an example, thecontrol slot information may include only information concerning acurrent priority level and lower priority levels. In a further example,the mesh node may schedule higher priority traffic in initial schedulingiterations and lower priority traffic in later scheduling iterations.

The mesh node may also receive one or more signals regarding an initialpreamble length. The mesh node may adjust a preamble based on a timebetween a last packet transmission and a current packet transmission toa neighboring node. The mesh mode may then send transmissions using theadjusted preamble to at least one neighboring node. In an example, thesignals regarding an initial preamble length may be received from acentral node. In a further example, the preamble length may be based onthe content of the transmission. Also, the mesh node may further adjustthe preamble based on estimated channel conditions for at least oneneighboring node. If the mesh node receives an acknowledgement, the meshnode may send further transmissions using the adjusted preamble. If themesh node fails to receive an acknowledgement, the mesh node may sendfurther transmissions using a preamble longer than the adjustedpreamble.

An mmH node may transmit a plurality of beacons during a beacontransmission interval. Each of the beacons may be transmitted in adifferent transmit antenna direction and separated by a beacon switchinterframe spacing (BSIFS). The node may receive a plurality of beaconresponses, each separated by a long interframe spacing (LIFS). The nodemay then transmit a beacon acknowledgment message in response to atleast one of the beacon responses. The beacon acknowledgment message maybe separated from the last beacon response by an LIFS.

In an additional embodiment, an mmH node may receive a control slotassignment for communication with a neighbor node and an indication ofan initial direction for communication. The node may transmit a requestto the neighbor node during the assigned control slot for a data slotfor a subsequent transmission to the neighbor node and may receive aresponse from the neighbor node that includes a data slot for thesubsequent transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A;

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A;

FIG. 1D is a system diagram of an example of a small-cell backhaul in anend-to-end mobile network infrastructure;

FIG. 2 is a diagram of an example superframe structure;

FIG. 3 is a diagram of an example Beacon Period;

FIG. 4 is a diagram of an example beacon transmission interval (BTI)slot (BTI_S);

FIG. 5 is a diagram of an example beacon response interval (BRI) slot(BRI_S);

FIG. 6 is a diagram of an example beacon response acknowledgement (BRA)slot (BRA_S);

FIG. 7 is a diagram of an example BTI preamble;

FIG. 8 is a diagram of an example BRI preamble;

FIG. 9 is a diagram of an example BRA preamble;

FIG. 10 is a diagram of an example process for coding and modulation forbeacon messages;

FIG. 11 is a diagram of an example scheduling interval (SI);

FIG. 12 is a diagram of an example control period structure;

FIG. 13 is a diagram of an example control slot structure;

FIG. 14 is a diagram of an example preamble for control messages 1 and2;

FIG. 15 is a diagram of an example preamble for control message 3;

FIG. 16 is a diagram of example control slot messages;

FIG. 17 is a diagram of an example high level message processing blockdiagram;

FIG. 18A is a diagram of an example of encoding for control messagesusing MinZeroPad;

FIG. 18B is a diagram of an example of decoding for control messagesusing MinZeroPad;

FIG. 19A is a diagram of an example encoding for control messages usingMinCodeRate;

FIG. 19B is a diagram of an example decoding for control messages usingMinCodeRate;

FIG. 20 is a diagram of an example long control message scrambler;

FIG. 21 is a diagram of an example iterative resource schedulingmechanism;

FIG. 22 is a diagram of an example process flow for performing resourcescheduling using the resource scheduling mechanism;

FIG. 23 is a diagram of an example control slot assignment with adifferent number of control slots for different neighbors;

FIG. 24 is a diagram of an example of iterative scheduling withinsufficient control slots;

FIG. 25 is a diagram of an example Control Slot Reassignment procedure;

FIG. 26 is a diagram of an example node mesh topology with variablecontrol period sizes;

FIG. 27 is a diagram of an example of Data Period Structure;

FIG. 28 is a diagram of an example Data Preamble;

FIG. 29 is a diagram of example data slot scenarios for N_(cs) equal to5 and no beam refinement;

FIG. 30A is a diagram of example encoder bit handling for low MCS;

FIG. 30B is a diagram of example decoder bit handling for low MCS;

FIG. 31 is diagram of an example Packet Delivery Time Probability withHARQ/ARQ;

FIG. 32A is a diagram of an example of a variable-length preamble;

FIG. 32B is a diagram of another example of a variable-length preamble;

FIG. 33 is a diagram of an example distribution of peak correlations tothe IEEE 802.11ad Golay codes.

FIG. 34 is a diagram of an example result from a simulation;

FIG. 35 is a diagram of an example result from a simulation;

FIG. 36 is a diagram of another example result from a simulation;

FIG. 37 is a diagram of an example result from yet another simulation;

FIG. 38 is a diagram of an example of another result from anothersimulation;

FIG. 39 is a diagram of an example result from yet another simulation;

FIG. 40 is a diagram of another example result from an additionalsimulation;

FIG. 41 is a diagram of an example comparison of the results ofsimulations; and

FIG. 42 is a diagram of an example comparison of multiple simulations.

DETAILED DESCRIPTION

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, 102 d, a radioaccess network (RAN) 104, a core network 106, a public switchedtelephone network (PSTN) 108, the Internet 110, and other networks 112,though it will be appreciated that the disclosed embodiments contemplateany number of WTRUs, base stations, networks, and/or network elements.Each of the WTRUs 102 a, 102 b, 102 c, 102 d may be any type of deviceconfigured to operate and/or communicate in a wireless environment. Byway of example, the WTRUs 102 a, 102 b, 102 c, 102 d may be configuredto transmit and/or receive wireless signals and may include userequipment (UE), a mobile station, a fixed or mobile subscriber unit, apager, a cellular telephone, a personal digital assistant (PDA), asmartphone, a laptop, a netbook, a personal computer, a wireless sensor,consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106, the Internet 110,and/or the other networks 112. By way of example, the base stations 114a, 114 b may be a base transceiver station (BTS), a Node-B, an eNode B,a Home Node B, a Home eNode B, a site controller, an access point (AP),a wireless router, and the like. While the base stations 114 a, 114 bare each depicted as a single element, it will be appreciated that thebase stations 114 a, 114 b may include any number of interconnected basestations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 114 a and/or the base station 114 b may beconfigured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 114 a may be divided intothree sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple-output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, etc.). Theair interface 116 may be established using any suitable radio accesstechnology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed DownlinkPacket Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (i.e.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1×, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A,the base station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106.

The RAN 104 may be in communication with the core network 106, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (VoIP) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. For example, the core network 106may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it will be appreciatedthat the RAN 104 and/or the core network 106 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 104 or a different RAT. For example, in addition to being connectedto the RAN 104, which may be utilizing an E-UTRA radio technology, thecore network 106 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102 a,102 b, 102 c, 102 d to access the PSTN 108, the Internet 110, and/orother networks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 112 may include wired or wireless communications networks ownedand/or operated by other service providers. For example, the networks112 may include another core network connected to one or more RANs,which may employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 130, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive RF signals. In another embodiment, the transmit/receiveelement 122 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 122 may be configured totransmit and receive both RF and light signals. It will be appreciatedthat the transmit/receive element 122 may be configured to transmitand/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station (e.g., base stations 114 a, 114 b) and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It will be appreciated that the WTRU 102 mayacquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

As shown in FIG. 1C, the RAN 104 may include base stations 140 a, 140 b,140 c, and an ASN gateway 142, though it will be appreciated that theRAN 104 may include any number of base stations and ASN gateways whileremaining consistent with an embodiment. The base stations 140 a, 140 b,140 c may each be associated with a particular cell (not shown) in theRAN 104 and may each include one or more transceivers for communicatingwith the WTRUs 102 a, 102 b, 102 c over the air interface 116. In oneembodiment, the base stations 140 a, 140 b, 140 c may implement MIMOtechnology. Thus, the base station 140 a, for example, may use multipleantennas to transmit wireless signals to, and receive wireless signalsfrom, the WTRU 102 a. The base stations 140 a, 140 b, 140 c may alsoprovide mobility management functions, such as handoff triggering,tunnel establishment, radio resource management, traffic classification,quality of service (QoS) policy enforcement, and the like. The ASNgateway 142 may serve as a traffic aggregation point and may beresponsible for paging, caching of subscriber profiles, routing to thecore network 106, and the like.

The air interface 116 between the WTRUs 102 a, 102 b, 102 c and the RAN104 may be defined as an R1 reference point that implements the IEEE802.16 specification. In addition, each of the WTRUs 102 a, 102 b, 102 cmay establish a logical interface (not shown) with the core network 106.The logical interface between the WTRUs 102 a, 102 b, 102 c and the corenetwork 106 may be defined as an R2 reference point, which may be usedfor authentication, authorization, IP host configuration management,and/or mobility management.

The communication link between each of the base stations 140 a, 140 b,140 c may be defined as an R8 reference point that includes protocolsfor facilitating WTRU handovers and the transfer of data between basestations. The communication link between the base stations 140 a, 140 b,140 c and the ASN gateway 215 may be defined as an R6 reference point.The R6 reference point may include protocols for facilitating mobilitymanagement based on mobility events associated with each of the WTRUs102 a, 102 b, 100 c.

As shown in FIG. 1C, the RAN 104 may be connected to the core network106. The communication link between the RAN 104 and the core network 106may defined as an R3 reference point that includes protocols forfacilitating data transfer and mobility management capabilities, forexample. The core network 106 may include a mobile IP home agent(MIP-HA) 144, an authentication, authorization, accounting (AAA) server146, and a gateway 148. While each of the foregoing elements aredepicted as part of the core network 106, it will be appreciated thatany one of these elements may be owned and/or operated by an entityother than the core network operator.

The MIP-HA may be responsible for IP address management, and may enablethe WTRUs 102 a, 102 b, 102 c to roam between different ASNs and/ordifferent core networks. The MIP-HA 144 may provide the WTRUs 102 a, 102b, 102 c with access to packet-switched networks, such as the Internet110, to facilitate communications between the WTRUs 102 a, 102 b, 102 cand IP-enabled devices. The AAA server 146 may be responsible for userauthentication and for supporting user services. The gateway 148 mayfacilitate interworking with other networks. For example, the gateway148 may provide the WTRUs 102 a, 102 b, 102 c with access tocircuit-switched networks, such as the PSTN 108, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and traditionalland-line communications devices. In addition, the gateway 148 mayprovide the WTRUs 102 a, 102 b, 102 c with access to the networks 112,which may include other wired or wireless networks that are owned and/oroperated by other service providers.

Although not shown in FIG. 1C, it will be appreciated that the RAN 104may be connected to other ASNs and the core network 106 may be connectedto other core networks. The communication link between the RAN 104 theother ASNs may be defined as an R4 reference point, which may includeprotocols for coordinating the mobility of the WTRUs 102 a, 102 b, 102 cbetween the RAN 104 and the other ASNs. The communication link betweenthe core network 106 and the other core networks may be defined as an R5reference, which may include protocols for facilitating interworkingbetween home core networks and visited core networks.

Other networks 112 may further be connected to an IEEE 802.11 basedwireless local area network (WLAN) 160. The WLAN 160 shown here may bedesigned to implement the modified features of the present application.The WLAN 160 may include an access router 165. The access router maycontain gateway functionality. The access router 165 may be incommunication with a plurality of access points (APs) 170 a, 170 b. TheAPs 170 a, 170 b may be configured to perform the methods describedbelow. The communication between access router 165 and APs 170 a, 170 bmay be via wired Ethernet (IEEE 802.3 standards), or any type ofwireless communication protocol. AP 170 a is in wireless communicationover an air interface with WTRU 102 d. WTRU 102 may be an IEEE 802.11STA, and may also be configured to perform the methods described herein.

FIG. 1D is a diagram of an example of a small-cell backhaul in anend-to-end mobile network infrastructure. A set of small-cell nodes 152a, 152 b, 152 c, 152 d, and 152 e and aggregation points 154 a and 154 binterconnected via directional millimeter wave (mmW) wireless links maycomprise a “directional-mesh” network and provide backhaul connectivity.For example, the WTRU 102 may connect via the radio interface 150 to thesmall-cell backhaul 153 via small-cell 152 a and aggregation point 154a. In this example, the aggregation point 154 a provides the WTRU 102access via the RAN backhaul 155 to a RAN connectivity site 156 a. TheWTRU 102 therefore then has access to the core network nodes 158 via thecore transport 157 and to internet service provider (ISP) 180 via theservice LAN 159. The WTRU also has access to external networks 181including but not limited to local content 182, the Internet 183, andapplication server 184. It should be noted that for purposes of example,the number of small-cell nodes 152 is five; however, any number of nodes152 may be included in the set of small-cell nodes.

Aggregation point 154 a may include a mesh gateway node. A meshcontroller 190 may be responsible for the overall mesh network formationand management. The mesh-controller 190 may be placed deep within themobile operator's core network as it may responsible for only delayinsensitive functions. In an embodiment, the data-plane traffic (userdata) may not flow through the mesh-controller. The interface to themesh-controller 190 may be only a control interface used for delaytolerant mesh configuration and management purposes. The data planetraffic may go through the serving gateway (SGW) interface of the corenetwork nodes 158.

The aggregation point 154 a, including the mesh gateway, may connect viathe RAN backhaul 155 to a RAN connectivity site 156 a. The aggregationpoint 154 a, including the mesh gateway, therefore then has access tothe core network nodes 158 via the core transport 157, the meshcontroller 190 and to ISP 180 via the service LAN 159. The core networknodes 158 may also connect to another RAN connectivity site 156 b. Theaggregation point 154 a, including the mesh gateway, also may connect toexternal networks 181 including but not limited to local content 182,the Internet 183, and application server 184.

As used herein, control region may refer to a control period and theseterms may be used interchangeably. Further, as used herein, schedulingiteration may refer to an scheduling interval (SI) and these terms maybe used interchangeably.

Densification of cellular networks may help meet a growing demand forincreased capacity, but may also require an increase in backhaulcapabilities. The Millimeter Wave Hotspot (mmH) project may use highlydirectional millimeter (mm) wave (mmW) links between these small-cellnodes to meet backhaul requirements. Unlike other mmW and microwave peerto peer (P2P) systems, the mmH backhaul may comprise a flexible meshnetwork employing electrically steerable mmW antennas. The electricallysteerable antennas may enable low cost, flexible, self-configuringbackhaul networks. The wide bandwidths in the mmW spectrum may enablevery high data rates. The high directionality of the antennas may implylow interference but also may present challenges to mesh networkoperation. The proposed mmH system can utilize elements of the currentIEEE 802.11ad standard as a baseline for the system design. However,various enhancements and modifications may be preferred beyond what isspecified in the standard and several example physical layer (PHY)modifications and other modifications are disclosed herein.

Example PHY modifications are disclosed herein and include thefollowing. Modified modulation and coding sets (MCSs) may enable longerrange communications at the minimum required data rate (referred to as alow MCS). A regular periodic superframe structure may enablecellular-like contention free access, long range discovery, and topologyformation. Modified beacon and beacon response messages may enable longrange discovery with high gain directional antennas on both ends of alink. An SI frame may consist of control slots for exchanges of controlmessages on a per link basis to negotiate scheduling of data, and dataslots (following the control slots) for the scheduled data transmission.

Example signaling to support fast hybrid automatic repeat request (HARQ)is described herein. It may be difficult to achieve the low latency andhigh throughput requirements over a multi-hop network. To help achievethis, fast re-transmissions with re-transmission combining areintroduced. Modified preambles, coding and modulation schemes, and Golaycodes are also supported. In many cases, the preambles may be shorteneddue to the stability of backhaul links and the way in which the linksare maintained in the backhaul mesh system.

Modified coding and modulation schemes are introduced to support themodified control and beacon messages (as well as the modified low MCS).Long low-density parity-check codes (LDPCs) may be applicable tobackhaul and known to have better performance. In examples, these aredisclosed herein for data packets.

The preambles used in the mmW backhaul system may be constructed ofGolay sequences similar to IEEE 802.11ad, but may be modified to enablea node to screen out (or fast detect) IEEE 802.11ad transmissions.Furthermore, the system may be configured to use a different set ofGolay codes to further mitigate interference between IEEE 802.11adnetworks as well as other from other nodes in own or other mm backhaulnetworks

Since highly directional antennas may be used on a limited set of links,the backhaul system may be predominantly noise limited. Therefore, powercontrol may be mainly geared towards limiting the received power to notgo much beyond that require by the largest MCS. Initial power controlmay be conducted during discovery. Because there may be less opportunityfor scheduling around interference in control slots, control slot powercontrol may be based on the reliability of the control messages.

The examples disclosed herein capture a PHY design for mmW mesh networksintended to provide small-cell backhaul for dense deployments. The PHYdesign may be based on the IEEE 802.11 Directional Multi-Gigabitamendment, IEEE 802.11ad. Examples are described that may introducemodifications to the existing specifications to better enable theenvisioned directional mesh networks that are likely to be acceptable tothe IEEE 802.11 community, but still not impose severe limitation on theoverall directional mesh network performance.

The examples disclosed herein provide a preliminary PHY specificationthat may be capable of supporting the range and data rate requirementsof the mmW backhaul system. It also provides a preliminary PHYspecification that may be capable of supporting fully scheduleddirectional mesh networks.

The IEEE 802.11ad standard is used as a baseline for the newly proposedmmH backhaul system design. The required enhancements described hereinmay be summarized as follows.

A modified beacon period structure may include various enhancements toenable longer discovery and communication range, support mesh formation,and better support contention free access. A modified SI and controlperiod design may be used to maintain mesh links and negotiate datafield transmission-reception schedules. A shortened preamble design isin some cases allowable due to the inherent stability of the backhaullinks and because each mesh link is maintained by frequent controlmessage exchanges. A modified low MCS design may meet the requirementfor longer communication range. In an example, the 802.11ad MCS1 datarate may be higher than is required in many cases. Longer codewordsgenerally may have better performance and be also feasible in backhaulwhere there are generally larger amounts of data available per packet. Adata header for a data packet may require changes but may be of similarsize and performance of the 802.11ad SC header. Regarding HARQ andend-to-end latency, the multi-hop mesh network may need to have highreliability and low latency above the media access control (MAC) layer.Greater reliability may be provided through retransmissions, but thelatency requirements may leave little latency budget. Retransmissioncombining may help ensure few re-transmissions are needed.

Modified complementary Golay codes for the backhaul (BH) may minimizeinterference with the 802.11ad codes already in use in un-coordinated802.11ad networks and help mitigate interference between nodes of sameor other BH network. Finally, due to the inherent low interferencelikely in the mmW BH, links may be typically noise limited (or errorvector magnitude (EVM) limited). Furthermore, transmission and receptiondirections may be limited to those of a small set of semi-static links.Power control can be mostly limited to cases of receiver max powerlimits or cases of specific link-link interference, but may stillrequire enhancement to 802.11ad.

The various transmission periods mentioned above may be logicallyordered into a superframe. One of the major differences of the modifiedsuperframe compared to the unmodified 802.11ad superframe may be thescheduled transmission architecture adopted for the mmH project.

FIG. 2 is a diagram of an example superframe structure. In an example,the superframe structure 210, including a Beacon Interval 220, may besplit into two major components: a Beacon Period 230, which may be usedfor new node discovery, mesh formation, and other purposes, and an SI270 which may be used to negotiate the scheduling of data slot resourcesbetween connected nodes, and for data packet transactions.

As shown, each SI 240, 250 may be further split into a Control Period242, 252 and a Data Period, 244, 254. There may be multiple SIs 240, 250per superframe. Exemplary values for the various superframe timingparameters are listed in Table 1.

TABLE 1 Superframe Timing Parameters Parameter Value F_(C): SC chip rate1760 MHz T_(C): SC chip time 0.57 ns = 1/F_(C) T_(BP): Beacon Periodduration 0.5 ms = 880000*T_(C) T_(SI): Scheduling Interval duration 0.5ms = 880000*T_(C) N_(SI): Max. Number of Scheduling ConfigurableIntervals per Beacon Interval [1 . . . 999] T_(BI): Beacon Intervalduration (T_(BP) + N_(SI)* T_(SI)) = (Superframe Duration) [1.0 ms . . .0.5 s]

The Beacon Period 230 may be composed of a beacon followed by possiblemessage exchanges in response to beacon reception. A further BeaconPeriod 260 may follow Beacon Period 230. The Beacon Period 230 may beused for long range node discovery, node configuration, node admission,and mesh formation. Since the system may intend to make use of very highantenna gains for long range communications and not place a bound on themaximum gain, the discovery procedure may make use of high gain antennasat both the transmitter and the receiver. This may require a modifiedsearch algorithm compared to IEEE 802.11ad which does not simultaneouslyuse high gain antennas at transmission (Tx) and reception (Rx).

FIG. 3 is a diagram of an example Beacon Period. As shown in thetransmissions 300, the Beacon Period 310 may be split into three majorcomponents: a Beacon Transmission Interval (BTI) 320, a Beacon ResponseInterval (BRI) 330, and a Beacon Response Acknowledgement (BRA) 340.Each BTI may be split into multiple BTI slots 323, 325, 329 which mayeach be separated by the Beacon Switch Inter-Frame Spacing (BSIFS) 324,326 to facilitate antenna beam direction switching between beacontransmissions. The space may be kept short (˜500 nSec) since suchswitching should be achievable. In an example, digital controlinterfaces and network architectures may need to be created to enablethis fast switching, e.g., phase shift values for all phase shifters inthe phased array antenna (PAA) could be preloaded in look-up tables(LUTs) and triggered by a fast event trigger. Further, a BTI slot(BTI_S) 322 may contain a BTI slot data (BTI_SD) 323 and a BSIFS 324.

Attached nodes may transmit the beacon message over multiple transmitantenna directions, one direction per BTI_S. The sweep over directionsmay not be completed in one BTI, but may require multiple BTI's. Theantenna gain may not be the maximum gain possible with the used antenna.If the size of the antenna is large compared to that required todiscover at the maximum distance, the antenna beam may be widened sothat the total sweep time to cover the full sweep range is reducedcompared to the maximum gain beam. The search pattern may be determinedto cover the full search range with no more than Ksearch dB (e.g., 3 dBfor Tx and Rx antennas) loss due to Tx and Rx antenna pointing errorwith a minimal number of beams. New nodes may listen for beacon messagein one particular receive antenna direction for each Beacon Interval.

The BRI 330 may be similarly split into slots 334, 336, 339 andseparated by a Long Inter-Frame Spacing (LIFS) 333, 335, 337 to accountfor a range of propagation delays for the new node response. The nodewishing to join the network may respond to only the node that providedthe best signal strength over its listening period and may use the Txbeam that is its best estimate of the best beam to use based on the Rxbeams it used to listen for the BTI. Further, a BRI slot (BRI_S) 332 maycontain an LIFS slot 333 and a BRI slot data (BRI_SD) 334.

The attached node may sweep its ‘listening’ Rx beam directions in thesame order that was used when transmitting in the BTI during the BRI.The new node may have the option to transmit in one or multiple slotsfor the response message. For the one slot example, the new node maytransmit the response in only the slot that corresponds to the attachednode's transmit direction that resulted in the best received beacon. Theone slot example may be used when the new node estimates that any misscalibration between the Tx and Rx beam directions (at its own PAA and anattached node's PAA) or asymmetry between Tx and Rx beam capabilitieswould not affect the choice of the best beam of the attached node torespond on.

For the multiple slot example, the new node may transmit the response inmultiple slots. This mode may be used when the choice of the best beamto respond on is uncertain (e.g., received signal strength indicators(RSSIs) from multiple directions are within a certain tolerance). Inthis case, the node may respond on up to three BRI_Ss. For example, thenode may respond on BRI_S 332 and two other BRI_Ss.

A final BSIFS 349 at the end of the Beacon Period allows the mesh nodeto re-orient its beam for the next message transmission. Attached nodesmay transmit any beacon acknowledge messages with the best beamestimated from any BRI responses received. The attached node may nottransmit a BRA if no BRI messages are correctly decoded. If BRI messagesfrom one or more new nodes are correctly decoded, the attached node mayrespond for a BRA in the next BRA opportunity to one of the new nodes.If BRIs from multiple new nodes are detected, the beacons may bemodified to indicate to new nodes that the expected BRA timing ischanged. New nodes may listen for a beacon acknowledge message in thesame receive antenna direction used to identify the best beacon.

FIG. 3 shows how the various Beacon Intervals may be further split intoBeacon Slots, as described above. Further, a BRA slot (BRA_S) 342 maycontain an LIFS slot 343 and a BRA slot data (BRA_SD) 344. The BeaconIntervals may be split into varying number of Beacon slots. In anexample, the number of BTI and BRI slots may determine the maximumnumber of sectors that may be swept through in one Beacon Period.

FIG. 4 is a diagram of an example BTI_S. In an example, the BTI_S 410may be split into a BTI preamble section 420, a BTI data section 430,and finally end with a BSIFS section 440. In a further example, theBTI_SD (not shown) may contain the BTI preamble section 420 and the BTIdata section 430.

FIG. 5 is a diagram of an example BRI_S. The BRI_S 510 may be similar tothe Beacon Transmission slots except that they may lead with theinterframe spacing section, LIFS 515. For example, the BRI_S may containan LIFS 515, a BRI Preamble 520 and BRI Data 530. In a further example,the BRI_SD (not shown) may contain the BRI Preamble 520 and BRI Data530.

FIG. 6 is a diagram of an example BRA_S. The BRA_Ss slots may be similarto the BTIs except that they lead with the beacon long interframespacing section (BLIFS) 615. As an example, the BRA_S may contain aBLIFS 615, a BRA Preamble 620 and a BRA Data 630. In a further example,the BRA_SD (not shown) may contain the BRA Preamble 620 and BRA Data630. Lastly, the Beacon Period may end with a final interframe spacing,a BSIFS 640 separating the Beacon Period from the SI. Exemplary valuesfor the timing parameters related to FIGS. 3, 4, 5 and 6 are shown inTable 2.

TABLE 2 Beacon Period Timing Parameters Parameter Value N_(BTI) _(—)_(S) = N_(BRI) _(—) _(S): Number of Beacon 22 Transmission and BeaconResponse slots in a Beacon Period T_(BTI) _(—) _(P): Duration of BeaconTransmission 7552*T_(C) Preamble T_(BTI) _(—) _(D): Duration of BeaconTransmission 7168*T_(C) Data T_(BTI) _(—) _(S): Duration of BeaconTransmission 15744*T_(C =) T_(BTI) _(—) _(P) + Slot T_(BTI) _(—) _(D) +BSIFS T_(BRI) _(—) _(P): Duration of Beacon Response 3328*T_(C) PreambleT_(BRI) _(—) _(D): Duration of Beacon Response 7168*T_(C) Data T_(BRI)_(—) _(S): Duration of Beacon Response 23120*T_(C =) LIFS + Slot T_(BRI)_(—) _(P) + T_(BRI) _(—) _(D) T_(BRA) _(—) _(P): Duration of BeaconResponse 3328*T_(C) Acknowledgement Preamble T_(BRA) _(—) _(D): Durationof Beacon Response 7936*T_(C) Acknowledgement Data T_(BRA) _(—) _(S):Duration of Beacon Response 26016*T_(C =) BLIFS + Acknowledgement SlotT_(BRA) _(—) _(P) + T_(BRA) _(—) _(D) + BSFIS T_(BTI): Duration ofBeacon Transmission (N_(BTI) _(—) _(S) * T_(BTI) _(—) _(S) − IntervalBSIFS) = 345344*T_(C) T_(BRI): Duration of Beacon Response (N_(BRI) _(—)_(S) * T_(BRI) _(—) _(S)) = Interval 508640*T_(C) T_(BRA): Duration ofBeacon Response (T_(BRA) _(—) _(S +) BSIFS) = Acknowledgement Interval26016*T_(C) BSIFS: Beam Switch Inter-Frame Spacing 1024*T_(C) LIFS: LongInter-Frame Spacing 12624*T_(C)  BLIFS: Long Inter-Frame Spacing13728*T_(C)  T_(BP): Beacon Period duration 0.5 ms = 880000*T_(C)

The beacon transmissions in the BTI may be the only messages in thesystem that may be received without the benefit of some timinginformation. In this way, the modified short training field (STF)requirements may be similar to that of unmodified 802.11ad. A Start ofPacket (SoP) may be detected without benefit of a schedule. Furthermore,there may be no historical reception of packets on which some initialautomatic gain control (AGC) or carrier frequency offset (CFO)estimation could be done. However, the IEEE 802.11ad Control PHY (C-PHY)preamble may not be reused since it may allow the new node attempting tojoin a mesh BH system to waste time receiving IEEE 802.11ad beacons.

FIG. 7 is a diagram of an example BTI preamble. The preamble shown in700 may use both the Ga 752, 754 and Gb 751, 753 sequences in the STF.The last pair is inverted to mark the end of beacon STF and still use−Ga as the prefix of the channel estimation (CE) field (CEF) 760. The Gaand Gb Golay sequences may also be replaced with other modified Golaysequences with low cross correlations to other Golays used in IEEE802.11ad as described below. These sequences may also be longer (e.g.,256 bits rather than 128 bits). The specific sequence to use isindicated in the BRA. By modifying the BTI preamble 710 as below, use ofthe IEEE 802.11ad Golay sequences for Ga and Gb (and other sequences)may remain possible, but selection of modified sequences may bepreferable.

FIG. 8 is a diagram of an example BRI preamble. The BRI preamble 800 mayuse both the Ga 852, 854 and Gb 851, 853 sequences, and may contain aCEF 860. Unlike the beacon transmission messages, the beacon responsemessages may be received after some timing information has been gainedin the BTI. This may allow for a relatively shortened STF period asshown in 800. The BRI preamble duration 810 may have the same durationas one of the 802.11ad preambles, but again may have different structureto permit distinction in the case that 802.11ad sequences are re-used.

FIG. 9 is a diagram of an example BRA preamble. The BRA preamble 900 mayuse both the Ga 952, 954, and Gb 951, 953 sequences, and may contain aCEF 960. The beacon acknowledge message may use the same preamble as thebeacon response messages since it may also have some prior timinginformation when it is received. In an example, the BTI preambleduration 910 may be the same as the BRA preamble duration 810.

Each beacon period may consist of three beacon message types exchangedbetween an attached node (A) and new node (B). The BTI message may betransmitted from the attached nodes to the new nodes, (A→B). Elements ofthe BTI message are described in Table 3. The BRI message may betransmitted from the new nodes to the attached nodes, (B→A). It may usethe same Golay sequence set that was received in BTI. Elements of theBRI message are described Table 4. The BRA message may be transmittedfrom the attached nodes to the new nodes, (A→B). Exemplary elements ofthe BRA message are described Table 5.

TABLE 3 BTI Message Size Order Field [Bits] Description 1 Network 16Full or partial network ID including ID operator ID. New node may usethis in PLMN selection and filtering 2 Node ID 12 ID of beacontransmitting node within the network. 3 Sector 8 ID of the beam beingtransmitted. Unique ID within the BTI, but non-unique between BTIs 4 Max8 Total number of sectors (or beams) that Sectors the beacontransmitting node may transmit to provide coverage over the sweep range5 Timestamp 8 Full or partial time information of the transmittedmessage to approx. 64 chip resolution. May be used to measure airpropagation time between message ex- changing nodes 6 Beacon 3 Indicatesthe next available BRI during Response which mesh node will listen fornew node's Offset Beacon response. The BRI immediately following thecurrent BTI may not be avail- able for new node response receptionbecause it may have been previously re- served for an associationprocedure with another new node, interference measure- ment, etc. 7 BRIuse 3 Indicates the purpose for subsequent BRI. code Valid codes mayinclude: available for new node beacon response (default), inter-ference measurement, other new node asso- ciation, etc. 8 Tx Power 12Beacon Tx power, EIRP. Max EIRP Info 9 Control 2 Number of control slotsper control period slots {5, 6, 7, 8} May alternatively go in the BRA 10Reserve 16 Reserved for future use 11 FCS 24 Frame Check CRC sequenceTotal 112

TABLE 4 BRI Message Size Order Field [Bits] Description 1 New node 48MAC address of the responding node. ID Network may check its databasefor node capabilities and if node may be admitted. 2 Additional 8Configured capabilities not learnable capability from MAC address classinfo 3 Mesh node 12 Beacon transmitting node's ID is ID echo echoed backto ensure that the pair are mutually ID'd. 4 Timestamp 8 Beacontransmitting node's Timestamp echo is echoed back so that airpropagation time may be computed. 5 Gateway 1 This may prevent a gatewaynode Indication from directly connecting to another gateway node. 6 RSSI4 Power of received beacon 7 Delta Rx 2 Difference between Rx gain andMax gain Rx gain 8 Reserve 13 Reserved for future use 9 FCS 16 FrameCheck CRC sequence Total 112

TABLE 5 BRA Message Size Order Field [Bits] Description 1 Node ID 12Responding node is given its node ID for this network. A node ID of 0 isnot accepted into network. If node is accepted, the following bits areinterpreted as: 2 Rx node 24 MAC address of receiving node ID echoechoed back to ensure mutual node (Hash) ID Hash of 48 bit address to 24bits. Hash function is TBD. 3 Time 8 Offset to apply when transmittingAdjust to this network node 4 Schedule 8 Indicator of control slots thenew node should initially listen to in linking to this network node 5Channel 2 Used to indicate a channel to use for initial schedule messageexchange. 6 Power 4 Power adjust for subsequent control adjust formessage transmission relative to control BRI messages 7 Configuration 12System information and new node message configuration data (e.g.,Channel Quality Indicator (CQI) table definition) 8 Initial 3 Indicatesto new node what control control slot to initially use on this link slot9 Reserve 15 Reserved for future use 10 Golay 4 Specifies a set of Golaysequences Sequence to use for Ga and Gb sequences. Indicator The GolaySequence Indicator may indicate what set the new node should use for itssubsequent transmissions on this link. 11 FCS 24 Frame Check CRCsequence Total 112

Coding and modulation of the BTI, BRI, and BRA (collectively called thebeacon messages) may be similar to C-PHY in 802.11ad, potentially makingit easier for a node to monitor/discover 802.11ad and mmW backhaulsimultaneously. The Beacon MCS (MCSB) may not need the same level ofprotection.

The beacon messages may be used during the discovery process before beamrefinement has taken place. Therefore, the full gain of the Tx and Rxantennas may not be assumed when estimating the discovery range. Thediscovery range should be commensurate with the low MCS communicationsrange and an antenna configuration to support that range. An exampledesired range for the low MCS may be 350 m. The discovery range may beat least this range when the same antenna configuration is used.

The required Rx power to reliably receive the beacon may be determinedas well (for instance, −70 dBm). However, there may be some differencesin the link budget assumptions. First, there may be an additional lossof about ˜6 dB to be added due to beam misalignment. Second, there is nostrong need to discover in heavy rain (25 mm/hr), which gives a 3.5 dBbenefit. The net result may be a loss of about 2.5 dB relative to theLow MCS. Since there is about an 8 dB difference in performance betweenthe low MCS and MCS0 in 802.11ad, there may be an ˜5.5 dB margin if MCS0is used for the beacon messages. The MCS0 data rate is howevercomparatively low (˜27.5 Mbps), and it may be beneficial to use some ofthat margin to reduce the beacon message duration. This may beaccomplished by modifying the IEEE 802.11ad MCS0. Possible methods mayinclude reducing the spreading factor from 32× to 16×, adding a parallelspreading code with 32× spreading, and using quadrature phase-shiftkeying (QPSK) modulation with 32× spreading.

While each method has it benefits and drawbacks, in an example, the QPSKbased method may be selected so that the effective symbol length of 32Tcmay be maintained, more than 3 dB signal to noise ratio (SNR) may beexpected to be required and Peak-to-Average Power Ratio (PAPR) may notbe degraded much. Parallel spreading may also be attractive. From workon the use of Golay sequences for the use in DS CDMA, it is known thatgood sets of spreading codes based on complementary Golay sequencesexist. A set of 32, 32-chip sequences may be found with very good mutualcorrelation properties. The set may be selected to also have goodcorrelation properties relative the IEEE 802.11ad Golay codes.

Other possible modifications include a reduction in payload compared tothe MCS0 1st LDPC codeword. This may provide some additional margin toeither extend the range slightly beyond the new low MCS range or permitwider beams to be used in the discovery process.

FIG. 10 is a diagram of an example process for coding and modulation forbeacon messages. At the beginning of an example process 1000, the beaconmessage 1010 may be scrambled 1015 starting with the 5th bit, where thescrambler may be initialized with {x1, x2, x3, x4, 1, 1, 1}. The resultis a sequence b 1020. The scrambled beacon message 1020 may be splitinto two equal length sequences b1 1022 and b2 1024 of length L. Eachsequence b1 1022 and b2 1024 may be padded with zeroes 1032 and zeroes1034 to a length of 504 total bits. The padded sequences may be codedwith the rate ¾ LDPC code to produce the code words C^(m)=(b^(m) ₁, . .. , b^(m) _(L), 0, . . . , 0, p^(m) ₁, . . . , p^(m) ₁₆₈), m={1, 2},which may include parity (P) bits 1044. The codewords may then have thezeros removed c¹=p¹ ₁, . . . , b¹ _(L), p¹ ₁, . . . , p¹ ₁₆₈,), c²=(b²₁, . . . , b² _(L), p² ₁, . . . , p² ₁₆₈). The two codewords c¹ and c²may be concatenated to create the sequence c³=(c¹, c²). The newsequence, c³, may be grouped into 2-bit symbols to create c⁴ _((k))=(c³_((2k-1)), c³ _((2k))). The sequence c⁴ _((k)) may then be convertedinto a complex data stream according to the mapping function

$\left\{ {{c^{4}(k)}\overset{f}{\rightarrow}{s(k)}} \right\}$given by the following:

$\left. {'{00'}}\rightarrow{\mathbb{e}}^{j\frac{\pi}{4}} \right.,\left. {'{01'}}\rightarrow{\mathbb{e}}^{j\frac{3\pi}{4}} \right.,\left. {'{11'}}\rightarrow{\mathbb{e}}^{{- j}\frac{3\pi}{4}} \right.,\left. {{{and}'}{10'}}\rightarrow{{\mathbb{e}}^{{- j}\frac{\pi}{4}}.} \right.$The pi/4 differential QPSK modulated signal, d(k), 1050 may then becreated as: d(k)=s(k)*d(k−1). In an example, d(0) may be defined to bee^(j0) so that the first symbol d(1)=s(1). The sequence may be spread1060 using the designated length 32 spreading codes to create:

$\begin{matrix}{{r(k)} = {{G_{a}\left( {\left( {k - 1} \right){mod}\; 32} \right)}{{d\left( \left\lfloor \frac{\left( {k - 1} \right)}{32} \right\rfloor \right)}.}}} & {{Equation}\mspace{14mu}(1)}\end{matrix}$

As stated above, one of the major differences in the mmH architecturecompared to the IEEE 802.11ad baseline is the use of a regularlyscheduled structure for multiple access as opposed to the contentionbased and contention free access methods specified for IEEE 802.11ad.Therefore, a modified scheduling period and data transfer period may berequired. This is referred to as a SI and may contain both a ControlPeriod and a Data Period.

FIG. 11 is a diagram of an example SI. The Control Period 1120 may beused to negotiate the scheduling of data slot resources between thevarious connected nodes. During each SI 1110 and for all nodes, a threemessage exchange may occur between the node and all of its neighbors.The exchange may include buffer status reports, grant requests, grants,channel quality information, Acknowledged (ACK)/Not Acknowledged (NACK)information and other information to assist in scheduling. Since failureto correctly decode control messages may result in no data slotgrant/allocation on a particular link as well as loss of linkmaintenance data, these messages may be provided with extra codingprotection relative to regular data transmissions.

The Control Period 1120 may be split into multiple Control Slots, 1121,1122 through 1129. The Data Period 1130 may be similarly split intomultiple Data Slots, 1131 through 1139 that may be allocated to thenodes based on the negotiating procedure defined in the Control period1120. Various exemplary timing parameters related to the SI are shown inTable 6.

TABLE 6 Scheduling Interval Timing Parameters Parameter Value N_(CS):Number of Control Slots per 5 default (configurable Control Period to 6,7, 8) N_(DS): Number of data slots per Data 32 Period T_(CP): Durationof Control Period Default 109952*T_(C) T_(DP): Duration of Data PeriodDefault 770048*T_(C) T_(SI): Duration of Scheduling Interval880000*T_(C) = T_(CP) + T_(DP) = 0.5 ms

FIG. 12 is a diagram of an example control period structure. In anexample each Control Period 1210 may be split into multiple ControlSlots, such that each node 1, 2 . . . N in the network may be assignedat least one Control Slot, 1221, 1222 . . . 1229 respectively, for eachof its connected neighbors. The Control Slots may be further split intothree sections to accommodate a three message exchange sequence. Anexample of a message exchange sequence is shown in FIG. 16.

FIG. 13 is a diagram of an example control slot structure. In anexample, each message may include a preamble section for synchronization1321, 1331, 1341, a data section 1322, 1332, 1342, and an interframespacing section 1324, 1334, 1344 used to avoid interference due topropagation delays. In an example, a data section 1322 may be a controlmessage. Finally, the figure also shows that the interframe spacingsection in the last Control Slot 1345 may be slightly longer than theothers which may result in the difference between Duration of ControlSlot 1315 and Duration of Last Control Slot 1310. Exemplary timingparameters for the default configuration of Number of Control Slots(NCS=5) are shown in Table 7.

TABLE 7 Default Control Period Timing Parameters Parameter Value N_(CS):Number of Control Slots per 5 Control Period T_(CP1): Duration ofControl Message 1 2304*T_(C) Preamble T_(CM1): Duration of ControlMessage 1 1088*T_(C) T_(CP2): Duration of Control Message 2 2304*T_(C)Preamble T_(CM2): Duration of Control Message 2 1600*T_(C) T_(CP3):Duration of Control Message 3  640*T_(C) Preamble T_(CM3): Duration ofControl Message 3 1088*T_(C) CIFS: Control Message Inter-frame4322*T_(C) Spacing CDIFS: Control Data Inter-frame 4324*T_(C) SpacingT_(CS): Duration of Control Slots 21990*T_(C)  (1: N_(CS) − 1) T_(CS)_(—) _(L): Duration of Last Control Slot 21992*T_(C)  T_(CP): Durationof Control Period 109952*T_(C) = T_(CS) * (See also Table 6) (N_(CS)− 1) + T_(CS) _(—) _(L)

As explained above, three separate messages may be defined in thecontrol period of the SI. The messages may be prepended with a preamblethat consists of both an STF and a CEF. One difference from theunmodified 802.11ad packet structure is that there may be no distinctionbetween the header and the data region. The number of SC-PHY data blocksassigned to the control messages may be Ncb(n), where n={1,2,3} toindicate the control message number. Ncb(n) may be system parametersthat are either fixed or are carried in the beacon or beacon ACKmessages. The major difference, however, has to do with the preamblesize, which may be shortened compared to the unmodified 802.11adpreamble size.

In the case of the first two messages the STF may be shortened.Specifically, control message 1 may have a shortened STF. Further,control message 2 may have a shortened STF.

FIG. 14 is a diagram of an example preamble for control messages 1 and2. The STF may be shortened for control messages 1 and 2, shown asmessage 1400, for several reasons. In an example, control messages 1 and2 may be shortened because the SoP detection may not be necessary sincethe beginning of the message packet, for example, Ga 1 1421, may bescheduled. However, some initial timing information may still berequired. The packet may start in parallel to the AGC (i.e., AGC doesnot need to be triggered by SoP since the schedule can trigger it).

In a second example, control messages 1 and 2 may be shortened and theAGC may not need to start from the beginning. Each link may be used ineach backhaul frame (every 0.5 mSec), and backhaul links may be prettystable, so one AGC cycle may be sufficient. In a further example, theremay be a wait for the gain to settle in Ga 2 1422. If the AGC keeps aper-link memory, the initial gain may not need to change much.

In a third example, control messages 1 and 2 may be shortened and clocksmay have less time to drift, so per-link CFO/sampling frequency offset(SFO) estimates may be maintained in much the same way as the AGC keepstrack of per-link gains. The exact length for CFO/SFO may vary, but mayuse six Ga sequences, for example Ga 3 1423 though Ga 8 1428 (2 lessthan Blu Wireless Technology (BWT)) The six Ga sequences may be used inexamples and simulations disclosed herein. In a further example, themessage may contain the fine packet timing and End of Short trainingField (EoSTF) of −Ga 9 1429 which may be followed by the CE field 1430.

FIG. 15 is a diagram of an example preamble for control message 3. Theexample depicts a preamble for control message 3 1500, where the STF maybe even further reduced and the CEF may be totally eliminated. Thisadditional shortening may be allowable since message 1 was received ashort time ago and the channel estimate, timing, and CFO are still good.However, some fine timing, CFO, and time offset/phase correction maystill be needed due to Tx/Rx switching, for example Ga 1 1521 through Ga4 1524, hence the inclusion of 5 Ga sequences for the preamble which mayfurther include the fine packet timing and EoSTF −Ga 5 1525.

Each node in the mesh network may be assigned at least one control slotfor each of its connected neighbors. Each such link defined between apair of neighbors may also be assigned an initial direction for controlmessage exchanges, for example, node A transmits to node B first.

FIG. 16 is a diagram of example control slot messages. The examplecontrol slot messages 1600 may be transmitted in sequence. At a highlevel the control slot messages may be as follows.

For control message 1 (A→B), Node A may request grant of data slots touse for a transmission to Node B. Node A may acknowledge the receptionof data from Node B in the previous SI. The example control message 1shown in FIG. 16 may be spread over two data blocks 1614 and 1616 basedon Table 15, and may be configurable as described in Table 15. The datablocks 1614 and 1616 may be surrounded by Guard Intervals (GIs).

For control message 2 (B→A) Node B may request grant of data slots touse for a transmission to Node A. Node B may acknowledge the receptionof data from Node A in the previous SI. Node B may grant resources toNode A based on the request from message 1. The example control message2 shown in FIG. 16 may be spread over three data blocks 1624, 1626 and1628 based on Table 15, and may be configurable as described in Table15. The data blocks 1624, 1626 and 1628 may be surrounded by GIs.

For control message 3 (A→B), Node A may grant resources to Node B basedon the request from message 2. The example control message 3 shown inFIG. 16 may be spread over two data blocks 1634 and 1636 based on Table15, and may be configured as described in Table 15. The data blocks 1634and 1636 may be surrounded by GIs.

The exemplary detailed message contents and the corresponding bitmapsare shown in Table 8, Table 9, and Table 10 for both high compressionand minimal compression options. Compression may refer to use of acompact notation that may limit the range of values that a signal mayindicate. If, for example, an error is detected in a message thatcarries grant request information (e.g., message 1 and message 2 carryBuffer Status Reports (BSRs), etc.) then a grant in the followingmessage may not be made and an indication of the frame check sequence(FCS) error may be included in the responding messages. An error indecoding message 1 or 2 may be signaled by sending all 1's in the Grantfield (an invalid Grant field) in message 2 or 3, respectively.

TABLE 8 Control Slot Message 1 (A → B) Minimal Compression Size Field[Bits] Description BSR 13 This is a resource request from A to B. (Usinga It may be signaled as a combination of LUT for requested data slotsand MCS/CQI where 3 QoS the last known good CQI indicates the queuesapprox. number of bits per data slot (a 0-32) default value may be usedif there is no last known good CQI). Resources may not be requested fordata that is expected to be transmitted in semi-statically scheduledresources. Note: For High Compression mode the available slot length mayalso be added. MCS/CQI  4 Estimate of the channel quality from Node B toNode A, and may be signaled in terms of a requested MCS level. Note: MCSlevels >12 may be reserved for indication of special purpose messages.Tx 32 Indication of available data slots for Bitmap Node A to transmitto Node B. Each bit may refer to a data slot. Note: For High Compressionmode this information is conveyed in the BSR. ACK 2 or 9 Node A mayacknowledge successful reception of data packets from B in the previousscheduling interval. Option 1 (default): [2 bits] 1-bit acknowledge forentire MAC Protocol Data Unit (MPDU) 1-bit acknowledge for persistenttraffic PHY Protocol Data Unit (PPDU) Option 2: [9 bits] 8-bitacknowledgement. 1-bit per PPDU, given maximum of 8 MPDUs per PPDU.1-bit acknowledge for persistent traffic PHY Protocol Data Unit (PPDU)FCS 12 Frame Check CRC sequence Total 63 or 70

TABLE 9 Control Slot Message 2 (B → A) Minimal Compression Size Field[Bits] Description BSR 13 This is a resource request from B to A. (Usinga It may be signaled as a combination of LUT for requested data slotsand MCS/CQI. 3 QoS Note: For High Compression mode the queues availableslot length is also added. 0-32) Tx 32 Indication of available dataslots for Bitmap Node B to transmit to Node A. Each bit refers to a dataslot. Note: For High Compression mode this information may be conveyedin the BSR. ACK 2 or 9 Node B may acknowledge successful reception ofdata packets from A in the previous scheduling interval. Option 1: [2bits] 1-bit acknowledge for entire MAC Protocol Data Unit (MPDU) 1-bitacknowledge for persistent traffic PHY Protocol Data Unit (PPDU) Option2: [9 bits] 8-bit acknowledgement. 1-bit per PPDU, given maximum of 8MPDUs per PPDU 1-bit acknowledge for persistent traffic PHY ProtocolData Unit (PPDU) Grant 32 Node B may grant data transmission slots toNode A based on its request and constraints due to previous allocationsto other nodes. Minimal Compression Mode Grant bitmap High CompressionMode Grant Start + Grant Length MCS/CQI  4 Estimate of the channelquality from Node A to Node B and may be signaled in terms of arequested MCS level. Note: MCS levels >12 may be reserved for indicationof special purpose messages. FCS 12 Frame Check CRC sequence Total 100or 107

TABLE 10 Control Slot Message 3 (A → B) Minimal Compression Size Field[Bits] Description Grant 32 Node A may grant data transmission slots toNode B based on its request and constraints due to previous allocationsto other nodes. Minimal Compression Mode Grant bitmap High CompressionMode Grant Start + Grant Length FCS 12 Frame Check CRC sequence Total 44

A Control Period does not exist in the current IEEE 802.11ad standard.Therefore, a modified coding method may be required for the messagesshown above. In an example, the coding method correlates well with the802.11ad baseline and at the same time meet the requirements of themodified control messages. For example, given the varying sizes for thethree control messages along with the relatively high level ofprotection required, the coding method may support a varying number ofpayload bits and code rates. The coding method also supports messagerepetition over a certain number of data blocks as well as messagesplitting across data blocks, which provides additional examples forpayload protection other than relying only on code rate choice.Exemplary parameters that relate to the various coding options are shownin Table 11.

TABLE 11 Coding Parameters Parameter Value Description Nmp 1-322 Numberof message payload bits Nrep 1-inf Number of additional data blocks usedwhen using message repetition. Nmf 1-322 Number of message fragmentsused when using message splitting. Nmfp 1-322 Number of message fragmentpayload bits in a particular message fragment. R [½, ⅝, LDPC mother coderate. ¾, 13/16] PuncMode [MinZeroPad, For a given Nmfp and choice of R,the MinCodeRate} PuncMode is given. Note: This allows proper ratematching to bring the 672 bits from the LDPC encoder into the 448 bitsavailable per data block. Nmfp_max Default is 110, Maximum number ofmessage fragment but can go as payload bits. much as 322

Both message splitting and message repetition may be used to offer moreprotection as mentioned above, however message splitting may be furtherrequired when {Nmp>Nmfp_max}. For example, if {Nmp>Nmfp_max}, themessage may be split into Nmf message fragments, where

$\begin{matrix}{{{Nmf} = \left\lceil \frac{Nmp}{Mmfp\_ max} \right\rceil},} & {{Equation}\mspace{14mu}(2)}\end{matrix}$and each message fragment of Nmfp bits may be coded separately, where

$\begin{matrix}{{{{Nmfp}(x)} = {\left\lfloor \frac{Nmp}{Nmf} \right\rfloor + \alpha}},} & {{Equation}\mspace{14mu}(3)} \\{\alpha = \left\{ {\begin{matrix}{1,} & {x = {1{\text{:}\mspace{14mu}\left\lbrack {\left( \frac{Nmp}{Nmf} \right) - \left( \left\lfloor \frac{Nmp}{Nmf} \right\rfloor \right)} \right\rbrack}{Nmf}}} \\{0,} & {x = {Nmf}}\end{matrix},{and}} \right.} & {{Equation}\mspace{14mu}(4)} \\{x = {1\text{:}\mspace{14mu}{{Nmf}.}}} & {{Equatio}\; n\mspace{14mu}(5)}\end{matrix}$For the case of {Nmp≤Nmfp_max}, Nmf=1.

Repetition, as stated, may be configured independently based on thedesire to add protection for the payload bits. For Nrep>0, theadditional data blocks may be constructed by creating another version ofthe codeword with different puncturing and inverting data blocks withodd repetition numbers, and concatenating them. In this sense, the ratematching block may produce two versions of the rate matched codewordthat the repetition block may alternate between.

Finally, for a given number of message fragment payload bits (Nmfp),different choices of R may be available with a corresponding puncturingmode. Representative options for each message fragment are given inTable 12.

TABLE 12 LDPC Code Rate and Puncture Mode Option per Message FragmentSize min max LDPC Code Rate [R] (Nmfp) (Nmfp) ½ ⅝ ¾ 13/16 1 56MinZeroPad MinZeroPad NA NA 57 98 MinCodeRate MinZeroPad MinZeroPad NA99 112 MinCodeRate MinCodeRate MinZeroPad MinZeroPad 113 140 NAMinCodeRate MinZeroPad MinZeroPad 141 161 NA MinCodeRate MinCodeRateMinZeroPad 162 280 NA MinCodeRate MinCodeRate MinCodeRate 281 322 NA NAMinCodeRate MinCodeRate

As shown in Table 12, certain exemplary combinations of message fragmentsize and code rate may be supported by a given puncture mode. The mainproperties of each of the puncturing modes may be as follows.

For the MinZeroPad, each 448-bit code block may be split into two224-bit parts. The systematic bits may be repeated twice, once in eachhalf of the 448-bit code block. Some of the parity bits may be repeateddepending on the number of systematic bits being used. The number ofparity bits repeated may be as many as all and as little as none. Inorder to obtain greater diversity in the repeated parity bits assumingthat Nrep>0, a puncture offset parameter, PO, may be defined such that adifferent combination of parity bits may be repeated for each repeatedcode block.

For the MinCodeRate, the 448-bit code blocks may not be split as in theMinZeroPad method. The parity bits may not be repeated. Some of thesystematic bits may be repeated depending on the number of parity bitsbeing used. The number of systematic bits repeated may be as many as alland as little as none. In order to obtain greater diversity in therepeated systematic bits assuming that Nrep>0, even numbered data blocksmay repeat the systematic bits starting at the beginning of the messageand odd numbered data blocks may repeat the systematic bits starting atthe end of the message.

Although exemplary minimum and maximum message fragment sizes may beextracted from Table 12, a more direct mapping of the representativesize range for each puncturing mode is shown in Table 13.

TABLE 13 Minimum and Maximum Message Fragment Sizes LDPC MinZeroPadMinCodeRate Code Min message Max message Min message Max message Ratesize size size size ½ 0 56 56 112 ⅝ 0 98 98 196 ¾ 56 140 140 280 13/1698 161 161 322

FIG. 17 is a diagram of an example high level message processing blockdiagram. In the example, the message is first fragmented 1710. Then theNmfp may be processed 1720 to create the LDPC codeword. The code rateand puncture mode may also be determined in 1730. Based upon thedetermined code rate and puncture mode, the LDPC processed messagefragments may be rate matched 1740. The output of which may be processedthrough a repetition step 1750. This may result in the data blocks to betransmitted.

FIG. 18A is a diagram of an example of encoding for control messagesusing MinZeroPad. Coding may be done on a per message fragment basis.The message fragments 1810 may first be encoded into the PHY bits of onesingle carrier (SC) block with N_(GI) symbols. The number of PHY bits ina SC block N_(CBPB) may depend on the modulation type, and exemplaryvalues are shown in Table 14. The number of SC blocks used for theentire transmission may be 1+N_(rep)(n) for message n. The bits may bescrambled and encoded as follows.

The input message bits including the FCS bits (b₁, b₂, . . . , b_(N)_(mfp) ), where N_(mfp) is the payload of the message fragment beingprocessed, may be scrambled as described below and illustrated in FIG.20 with the initialization vector (IV) given, starting from the firstbit, to create d_(1s)=(q₁, q₂, . . . q_(N) _(mfp) ). The LDPC codewordc=(q₁, q₂, . . . , q_(N) _(mfp) , 0₁, 0₂, . . . , 0_(Z), p₁, p₂, p_(N)_(p) ) may be created by concatenating Z zeroes 1820 to the N_(mfp) bitsof d_(1S) and then generating the parity bits 1830 p₁, p₂, p_(N) _(p)such that Hc^(T)=0, where H is the parity check matrix for the rate RLDPC code specified in IEEE 802.11ad. Note that Z=672R−N_(mfp) andN_(p)=672(1−R). Parity bits 1831, 1832, 1835, 1836 and 1837 may also beused.

In an example, a code rate ½ may be used for two repetitions (Rep=2) forK1=1-56. In a further example, code rate ½ may also be used for onerepetition (Rep=1) for K1=56-122, but a higher rate may also be used perTable 13 and the table in FIG. 18A. In an example, information bits K1may all be repeated. Further parity bits may be preferentially puncturedby placing the Puncture Offset (PO) to the right of the center of eachcodeword (CW). In FIG. 18A, P11 1831 may be a subset of P21 1836 and P221837 may be a subset of P12 1832. As a result, P11 1831 and P22 1837 maybe repeated bits. Although not illustrated in FIG. 18A and FIG. 18B,below, data scrambling, repetition scrambling and fragment concatenationmay apply to the encoding.

The Information Bits 1815 may be preserved whereas the zeroes 1825 maybe removed. Bits N_(mfp)+1 through 672R and the parity bits P0−PLthrough P0−1 of the codeword c may be removed to create the sequencecs1=(q₁, q₂, . . . , q_(N) _(mfp) , p₁, p₂, . . . , p_(P0−PL−1), p_(P0),. . . , p_(N) _(p) ) and then XORed with a pseudo-random noise (PN)sequence that is generated from the linear feedback shift register(LFSR) used for data scrambling defined in IEEE 802.11ad. The LFSR maybe initialized to the all ones vector. Bits N_(mfp)+1 through 672R andthe parity bits P0 through P0+PL−1 of the codeword c may be removed tocreate the sequence cs2=(q₁, q₂, . . . , q_(N) _(mfp) , p₁, p₂, . . . ,p_(Po-1), p_(P0+PL), p_(P0+PL+1), . . . , p_(N) _(p) ). Note that

$L = {N_{mfp} + {672\left( {1 - R} \right)} - \frac{N_{CBPB}}{2}}$ and${{{{P\; 0} - \frac{N_{P}}{2}}} + {PL}} < \frac{N_{P}}{\; 2}$may be satisfied.

The sequences cs1 and cs2 may be concatenated to form the sequence (cs1,cs2). The resulting N_(CBPB) bits may then be mapped as π/2−BPSK asdescribed in IEEE 802.11ad. The N_(GI) guard symbols may then beprepended to the resulting N_(CBPB) bits as described in IEEE 802.11ad.The results of the encoding may then be modulated and transmittedthrough the channel.

FIG. 18B is a diagram of an example of decoding for control messagesusing MinZeroPad. In an example, the process is effectively the reserveof the encoding process. Demodulation of the transmission results in asequence which may contain a number of copies of information bits andpunctured parity bit which corresponds to the number of repetitionsperformed in the encoding process. In an example, two informationmessages 1862 and 1864 may be included in the result of thetransmission. At the receiver, the logarithm likelihood ratios (LLRs)per bit may be available. The punctured parity 1870 may then berecombined. The combination may then be decoded with the LDPC decoder1880 and the parity may be further removed. The zeroes may then befurther removed leaving only the information bits 1890. The informationbits 1890 may then be sent to the cyclic redundancy check (CRC).

TABLE 14 Values of N_(CBPB) Modulation Type N_(CBPB) π/2 - BPSK 448π/2 - QPSK 896 π/2 - 16QAM 1792

Control message coding and modulation for the MinCoderate puncturingmethod is disclosed herein. Coding may be done on a per message fragmentbasis. The message fragments may first be encoded into the PHY bits ofone SC block with N_(GI) symbols. The number of PHY bits in a SC blockN_(CBPB) may depend on the modulation type, and exemplary values areshown in Table 14. The number of SC blocks used for the entiretransmission may be 1+N_(rep)(n) for message n.

FIG. 19A is a diagram of an example encoding for control messages usingMinCodeRate. The example shows how MinCodeRate may scramble and encodemessage bits. The input message 1910 bits may include the FCS bits (b₁,b₂, . . . , b_(N) _(mfp) ), where N_(mfp) is the payload of the messagefragment being processed, and may be scrambled with the IV, as describedbelow and illustrated in FIG. 20. The scrambling may start from thefirst bit, to create d_(1S)=(q₁, q₂, . . . , q_(N) _(mfp) ).

The LDPC codeword c=(q₁, q₂, . . . , q_(N) _(mfp) , 0₁, 0₂, . . . ,0_(Z), p₁, p₂, p_(N) _(p) ) may be created by concatenating Z zeroes1920 to the N_(mfp) bits of d_(1s) and then generating the parity bitsp₁, p₂, p_(N) _(p) 1930 such that Hc^(T)=0, where H is the parity checkmatrix for the rate R LDPC code specified in IEEE 802.11ad. Note thatZ=672R−N_(mfp) and N_(p)=672(1−R).

Bits N_(mfp)+1 through 672R (the zero bits) may be removed to obtainc1=(q₁, q₂, . . . , N_(mfp) p₁, p₂, . . . , p_(N) _(p) ). Formod₂(N_(rep))=0, as described below and illustrated in FIG. 20 with theIV given, the method may remove and scramble the first N_(sysRep) bitsof the sequence c1. These bits may be appended to the beginning of c1 tocreate the sequence c2=(q^(s) ₁, q^(s) ₂, . . . , q^(s) _(NsysRep), q₁,q₂, . . . , q_(N) _(mfp) , p₁, p₂, . . . , p_(N) _(p) ). Otherwise, asdescribed below and illustrated in FIG. 20 with the IV given, the methodmay remove and scramble the last N_(sysRep) bits of the sequence c1.These bits may be appended to the beginning of c1 to create the sequence1940 c2=(q^(s) _(N) _(mfp) _(−N) _(sysRep) ₊₁, q^(s) _(N) _(mfp) _(−N)_(sysRep) , q^(s) _(N) _(mfp) , q₁, q₂, . . . , q_(N) _(mfp) , p₁, p₂, .. . , p_(N) _(p) ). For example

${N_{sysRep} = {{Z - \left( {672 - N_{CBPB}} \right)} = {{672R} - \frac{N_{CBPB}}{2} - N_{mfp}}}},{e.g.},{\left\{ {{{{For}\mspace{14mu} R} = \frac{1}{2}},{N_{sysRep} = {112 - N_{mfp}}}} \right\}.}$

The resulting N_(CBPB) bits may be multiplied with −1 mod₂(N_(rep))where N_(rep)=0, 1, . . . N_(rep)(n), and then mapped as π/2−BPSK asdescribed in IEEE 802.11ad. The N_(GI) guard symbols may then beprepended to the resulting N_(CBPB) bits as described IEEE 802.11ad. Theresulting sequence may then be appended after the sequence created forthe first data block. After modulation, the resulting sequence may thenbe transmitted through the channel.

In an example, a code rate ½ may be used for two repetitions (Rep=2) forK1=1-56. In a further example, code rate ½ may also be used for onerepetition (Rep=1) for K1=56-122, but other code rates are alsopossible. Further, in an example, the K2 bits may be copied from theleft.

FIG. 19B is a diagram of an example decoding for control messages usingMinCodeRate. The process for decoding is effectively the reverse ofencoding. After demodulation, the sequence may include the scrambledinformation 1951, the information bits that were not scrambled 1952 andthe parity bits 1953. The encoding process may then be further reversedresulting in information bits 1954. The sequence may then be decoded bythe LDPC decoder 1980 and the zeroes may be removed resulting ininformation bits 1990. The information bits may then be furtherdescrambled resulting in 1995. These bits may then be sent to the CRCand concatenated with any other message fragments.

The Coding and Modulation procedures described above may support avariety of message lengths. In addition, the coding procedure for eachmessage length may be further modified to support varying performancerequirements. As such, given the exemplary message lengths detailed inTables 8-10, simulations may be used to determine the particular codingand modulation parameters to be used.

The control messages may require high protection relative to regulardata transmissions. With this, in an example, a set of coding parametersmay give performance at least as good as the header performance shown inFIG. 42. Table 15 lists representative initial tentative coding optionsbased on example simulations performed. There are multiple viableoptions may be chosen and the specific option to be used may be signaledin the beacon period.

TABLE 15 Control Message Coding Parameters Number of Message CompressionPuncture Message Block Code Number Mode Mode Fragments Repetition Rate 1Minimal MinZeroPad 2 None ⅝ 2 Minimal MinZeroPad 3 None ½ 3 MinimalMinZeroPad 2 None ½

The control message scrambler may have a larger period than the normalheader/data scrambler. The larger length may provide a larger IV so thatevery message in a backhaul superframe may have a distinct IV. Forexample there may be 1000 frames/superframe, 5 control slots per frame,3 messages per control slot for a total of 15,000 control message persuperframe or 14 bits. Furthermore, offsets into the scrambler may bedesired that will not cause the scrambler to repeat its sequence. Theoffsets may provide distinct sequences based on the node or linkidentifications (IDs). In this way, two conditions may be satisfied. Inone example condition, the scrambling sequences may be well mixed overthe superframe. In another example condition, a node that is out of syncwith the network (e.g., using the wrong control slot) may have a lowprobability of falsely thinking it received a grant to transmit withoutexplicitly sending node IDs in the messages.

To accommodate a large number of local link identifiers, an additional10 bits of LFSR may be added. In some circumstances there may not be2-tap feedback solutions to the 24-bit m-sequence generator, a 25-bitLFSR may be defined with 2-taps (there may be two different 2-tap,25-bit LFSRs with maximal length sequences). One such example isprovided by the primitive polynomial: S(x)=x²⁵+x²²+1, and is illustratedin FIG. 20.

FIG. 20 is a diagram of an example long control message scrambler. Thecontrol message scrambler 2000 may include twenty-two delay units, suchas delay units 2010 through 2090. The control message scramblerinitialization 2000 may be determined by the following:IV=1+mod₂ ₂₅ ⁻¹(IV_(seed)+LOC_(rx) _(_) _(id) +m+3s+N _(a) b),  Equation(6)where IV_(seed) is an optional 5-bit parameter signaled in the beaconresponse ACK message and is a function of the beacon transmitter ID.LOC_(rx) _(_) _(id) may be a globally non-unique, but locally unique IDgiven to the new node used to distinguish nodes of the local mesh. Withscrambling based on LOC_(rx) _(_) _(id), the ID may not need to beexplicitly transmitted (message not decodable if different LOC_(rx) _(_)_(id) used). m is the Message Number−1 {0,1,2}. s is the Control SlotNumber−1, b is the SI (SI Number−1) {0, 1, . . . , 999}, and N_(s) isNumber of Control Slots.

A backhaul network requires support of service-level agreements (SLAs).In packet backhaul networks, these SLAs determine if the guaranteedthroughput and latency requirements are met. This may be achieved byutilizing committed information rate (CIR) and excess information rate(EIR) terminology.

CIR is the average guaranteed capacity to be given to a data flow undernormal conditions. Under operating conditions, the capacity should notfall below the CIR. EIR is the upper bound allowed above CIR rate. Inorder to provide differentiated services in the backhaul network,multiple classes of service or QoS are supported in the small-cellbackhaul network.

In order to maximize the amount of higher priority traffic fordirectional mesh backhaul networks, scheduling support may be requiredto enable iterative scheduling to achieve this in a purely distributedmanner. As a result, the directional mesh backhaul may be capable ofhandling bursty traffic while respecting the corresponding QoS/class ofservice.

In one embodiment, the total number of control slots (N) in the ControlPeriod may be determined a-priori, may be common to all the mesh nodesin the network and may remain constant for a specific configuration ofthe network. For a mesh node in the network with K neighbors, there areat most M=floor(N/K) complete iterations of control slots, where eachneighbor is allotted one control slot per iteration. This allows eachnode to exchange scheduling information with its neighbors more thanonce per SI. Each of these control slots may involve a three-way messageexchange between the nodes. The three-way message exchange was discussedabove.

As the number of control slots may be common for all mesh nodes in thenetwork, there may be instances where the number of neighbors may belower than the number of available control slots. The network may alsoconfigure more control slots than the highest number of possibleneighbors allowed for each mesh node to enable more than one exchange ofcontrol slot information in order to achieve better differentiated classof service and allocation of CIR data over EIR. This allows for thepossibility of iterative scheduling. Iterative scheduling enablespriority-based resource reservation to be performed dynamically in eachSI. If traffic priorities are known, then higher priority traffic may bescheduled in the initial scheduling iterations while lower priority datamay be scheduled in later scheduling iterations. If trafficclassification based on CIR and EIR labelling is available, then CIRtraffic may be scheduled in initial scheduling iterations followed byEIR traffic scheduling.

The multiple scheduling iterations may be used for prioritized resourcereservation in several different ways. In one embodiment, resourcerequests and schedules associated with one or few priority levels may beexchanged in a particular scheduling iteration. Here, resources may beallotted for high priority traffic first and then any remainingresources may be allotted to lower priority traffic. This may ensurethat all the nodes have exchanged required information about higherpriority traffic with their neighbors and may allow for this traffic tobe scheduled before allowing lower priority traffic, thereby avoidingreversal of traffic class/QoS prioritization.

In another example, mesh nodes may send their resource requests andtemporary schedules for all priorities in each scheduling iteration.Then, the receiver may determine the schedule for the current prioritylevel based on the received resource requests and previously scheduledresources for higher priority traffic. Fairness among different prioritylevels may be ensured by exchanging more information about differentpriority traffic in each scheduling iteration.

In another example, where information about current priority level andlower priorities may be exchanged, the control signaling overhead may bereduced. Further, the scheduling information exchanged may be in theform of bitmaps to reduce the message sizes, but this may eliminate thepriority information of previously scheduled traffic. Consequently, atrade-off is possible between control message overhead and trafficprioritization efficiency.

FIG. 21 is diagram of an example of an iterative resource schedulingmechanism. The resource scheduling mechanism 2100 may apply to controlslots, for example control slots in a control region 2110 or controlperiod. A data region 2120 may follow the control region 2110. Here, thecontrol region 2110 has sufficient control slots for M iterations 2111,2112 and 2119 of the scheduling algorithm. Each iteration 2111, 2112 and2119 may include a sufficient number of bi-directional control slots foreach mesh node to exchange scheduling information with each of itsneighbors. The exchange of scheduling information with each neighbor mayoccur in a three message sequence, including message 1 2131, message 22132 and message 3 2133. In an example, the neighbors may exchangecontrol slot information in this way. The number of control slots foriterative scheduling may vary from neighbor to neighbor. In an example,during consecutive periods, 2130, 2140, 2150, in algorithm iteration 12111, each node may communicate with a different one of its neighbornodes. For instance, in the period 2130, node G 2139 may exchangeinformation with neighbor node A 2134, Node B 2135 may communicate withneighbor Node E 2138 and Node C 2136 may communicate with neighbor NodeD 2137. All neighbors may not be allotted a control slot in eachscheduling iteration. The number of iterations for a particular neighbormay depend on the number of active traffic priority levels associatedwith it or the number of active neighbor nodes. In an exemplaryembodiment, signals, such as a control signal, are received by a meshnode from a mesh controller. Further, in an exemplary embodiment, theresource scheduling mechanism may include a resource schedulingalgorithm.

FIG. 22 is a diagram of an example process flow for performing resourcescheduling using the resource scheduling mechanism. In an example, theprocess 2200 may begin when a mesh node receives a control signal whichmay include the number of available control slots 2110. The controlsignal may be received from a mesh controller. The number of availablecontrol slots may be determined by the network. The node may thendetermine 2220 the number of iterations of a resource schedulingmechanism that can be made during the time period of the total number ofavailable control slots. The node may maximize the number of possibleiterations based on local topology. In an example, the node maydetermine the number of iterations based on the number of availableneighbor nodes for the mesh node. The node may then receive 2230 controlslot information from neighbor nodes. This information may includeinformation about one or more of traffic queues, priorities and channelconditions. The node may then perform resource scheduling 2240 using theresource scheduling mechanism. The resource scheduling may be based oncurrent control slot information, as well as control slot informationreceived in prior resource scheduling iterations. In a further example,the resource scheduling may also be based on current traffic informationand historic traffic loads.

FIG. 23 is a diagram of an example control slot assignment with adifferent number of control slots for different neighbors. It shows anexample where a mesh node may allocate a different number of schedulingiterations to different neighbors due to a varying neighbor count forone of the neighbors. Here, Node 2 2320 may not be accommodated in thesecond iteration by Node 1 2310 because there are no common controlslots between the two nodes that are unallocated slots, such as 2332.Further node 1 2310 may not communicate with node 2 2320 using its lastunallocated slot as node 2 has allocated node 7 for that slot. Thenumber of scheduling iterations and control slot allocations may bechanged between nodes by a control slot reassignment procedure describedbelow.

In an example, if there are insufficient slots in the control period fora complete iteration of the resource scheduling mechanism or schedulingalgorithm, then slots may be assigned to a sub-set of the neighbors. Asa result, resource scheduling may include maintaining relative fairness.

FIG. 24 is a diagram of an example of iterative scheduling withinsufficient control slots. In this example, the number of control slotsmay not be an exact multiple of the number of neighbors that a mesh nodehas. Here, the last two control slots are distributed among the threeneighbors and this distribution may be rotated in successive schedulingiterations to maintain relative fairness. The scheduling iterations mayinclude SIs, such as SIs 2410, 2420 and 2490. The control slotassignment may be pre-determined and communicated to all the affectednodes but may be changed occasionally due to topology or traffic patternchanges.

Mesh nodes may use the Control Slot Reassignment procedure to re-arrangecontrol slots allotted to their neighbors. This may be required when newnodes join the network, when there is node or link failure and when thenumber of priority levels used by the scheduling algorithm needs to bechanged. This may be accomplished by exchanging a series of messagesbetween the affected nodes.

The procedure may start with the requesting node sending a Control SlotReassignment Request message to the affected neighbors. The neighborsmay then respond with Control Slot Reassignment Response message, whichincludes information about their available control slots. The requestingnode may send a Control Slot Reassignment Confirm message to theneighbors with the new control slot assignments. The neighbors mayrespond with a Control Slot Reassignment Confirm message to confirmreceipt of the new assignment.

FIG. 25 is a diagram of an example Control Slot Reassignment procedure.In the example, Node 1 2510 has Nodes 2 2520 and Node 3 2530 asneighbors, and may send Control Slot Reassignment Requests 2551 and 2552to them, respectively, to initiate the procedure. Nodes 2 2520 and 32530 may respond with their available control slots in Control SlotReassignment Response frames 2556 and 2557 respectively. In thisexample, Node 1 2510 may send a New Slot Allocation 2559 to Node 3 2530,included in Control Slot Reassignment Confirm message, that may requireNode 3 2530 to further re-assign slots with its other neighbor, Node 42540. Consequently, Node 3 2530 may send Control Slot ReassignmentRequest 2561 to Node 4 2540 and complete the Slot Reassignmentcommunications with Node 4 2540 (Control Slot Reassignment Response2566, Control Slot Reassignment Confirm 2569 and Control SlotReassignment Confirm Result Code 2571), before responding to Node 1 2510with Control Slot Reassignment Confirm message 2573. Then, Node 1 maysend Control Slot Reassignment Confirm message 2581 to Node 2 2520,including New Slot Allocation 2581, and receive a Control SlotReassignment Confirm message 2583 with the ResultCode that indicates thestatus of the reassignment.

The Control Slot Reassignment procedure may also be utilized to revokeone or more control slots allocated to a neighboring node if the meshnode identifies that it needs to allocate these control slots to one ormore of its other neighbors or newly formed neighbors. In a furtherexample, the Control Slot Reassignment procedure may be coordinated by amesh controller, such as a Central Mesh Controller, by sendingappropriate messages to affected mesh nodes. This message may includetime instance at which the new configuration will take into effect.

Small-cells are expected to be rolled out first in dense urban and urbanenvironments. Given the varying landscape of dense urban and urbanenvironments, the small-cell mesh backhaul connectivity for each meshnode may vary significantly from one part of the network to the other.Configuring the entire mesh network with constant amount of controlslots may incur large overhead in parts of the network whereconnectivity is low. On the other hand, if fewer control slots are usedthroughout the network, this may artificially limit the number of linksa mesh node can form even though there are good quality links that canbe formed in certain parts of the network. To avoid this and to enableappropriate scaling of control period based on local mesh connectivityfor each mesh node, variable control periods may be used.

Different parts of the mesh network may use different number of controlslots, and consequently variable Control Period sizes. A Domain may bedefined as a contiguous collection of mesh nodes that share the sameControl Period size. At the boundary between different Domains may liemesh nodes that use different Control Period sizes to communicate withdifferent neighbors. Such mesh nodes may belong to more than one Domainas they need to communicate with mesh nodes that belong to two or moredomains.

A mesh network may start off with a default number of control slots thatmay be either pre-configured in the mesh nodes and read during start-up,or optionally communicated by the mesh controller, if one exists. Thedefault or initial Control Period size may be changed later either in adistributed manner or via central messaging. To change the ControlPeriod size in a distributed manner, the requesting node may send aControl Period Reconfiguration Request message to all or a subset of itsneighbors. The size change may be confirmed when the neighbors respondwith a Control Period Reconfiguration Confirm message. In thecentralized approach, the mesh controller may send Control PeriodReconfiguration Request message to all or some mesh nodes to change theControl Period size, by adding or removing control slots. The boundarynodes may use different number of control slots with neighbors belongingto different Domains.

FIG. 26 is a diagram of an example node mesh topology with variablecontrol period sizes. In an example, Node 1 2611 and Node 2 2612 maybelong to Domain 1 2610, while Node 4 2624 and Node 5 2625 may belong toDomain 2 2620. Node 3 2632 may belong to both Domain 1 2610 and Domain 22620. Nodes belonging to Domain 1 2610 may use 6 control slots 2613,while those belonging to Domain 2 2620 may use 8 slots 2634. Node 3 2633may use the first 6 control slots while communicating with nodesbelonging to Domain 1 2610 and may use all 8 control slots forcommunicating with nodes belonging to Domain 2 2620. Node 3 2633 may usethe time required for control slots 6 and 7 for data transmissionswithin Domain 1 2610, if they do not cause interference to ControlPeriod transmissions in Domain 2 2620. Alternatively, all Control Periodtransmissions may employ a low MCS for additional protection againstinterference. Node 3 2633 allots control slots to neighbors belonging toDomain 1 2610 (for example Node 2 2612) in the first 6 control slots.For neighbors belonging to Domain 2 2620 (for example Node 4 2624 andNode 5 2625), all 8 control slots may be used. Here two scheduling slotallocation options are shown. In another embodiment, the extra controlslots may be left vacant in Domain 2 2620.

The iterative scheduling defined above may be used in conjunction withvariable control period sizes to get the additional benefit ofdifferentiated service level scheduling. For instance, the extra slotsmay be used for scheduling Domain 2 2620 neighbors (for example Node 42624 and Node 5 2625), which may execute more iterations of thescheduling algorithm. This situation may arise if Node 3 2633 needsallocations for only two priority levels for Domain 1 2610 neighbors(hence two iterations of scheduling) and three priority levels forDomain 2 2620 neighbors. Another reason could be that some of the nodesin Domain 2 2620 may have more number of neighbors than those in Domain1 2610, hence requiring more number of control slots. The nodes may bereconfigure the control slot assignment using Control Slot Reassignmentprocedure 2500 either after or before changing the Control Period size,depending on whether the Control Period size is increased or decreased,respectively.

In a further example, the domains could also be structured to limit theimpact of interference of control slots in one domain towards another.In an example case, adjacent domains may have different control periodsizes and the data transfer in the domain with smaller control periodsize may impact the domain with relatively larger control period size.In order to achieve optimal allocation of domain and to manage theimpact of interference on control period, the centralized meshcontroller may trigger interference measurements at each of the meshnodes and to determine the interference zone of each mesh node. Theseinterference measurements may be configured so as to determine theimpact of interference of each link between a pair of mesh nodes onneighboring links within a conservative distance range and can befurther refined based on received measurement reports by the meshcontroller. Based on the received interference measurement report fromeach of the mesh nodes, the mesh controller may determine the domainsand what the control period size of each of the domains.

As shown in FIG. 11 each SI may contain both a Control Period and a DataPeriod. The Data Period may be further split into N_(ds) Data Slots,where one or more Data Slots are assigned for a particular packettransmission from a node. As will be explained below, these Data Slotsmay be structured differently based on the size of the packet beingdelivered. As shown in FIG. 27, the Data Period may contain thefollowing components: a preamble, described below, a header, and apayload. Certain fields in the header may require changes with respectto the unmodified IEEE 802.11ad SC packet. Examples of these changes aredetailed in Table 17 below. The payload may include LDPC coded data(possibly longer LDCP codewords, with respect to the unmodified IEEE802.11ad SC packet). Table 16 shows exemplary related timing parametersfor the default case of Ncs=5.

TABLE 16 Default Data Period Timing Parameters Parameter Value N_(DBM):Maximum Number of Data Blocks 47 in a Data Slot (Refer to FIG. 23)T_(DPR): Duration of Data Preamble 2048*T_(C) T_(DH): Duration of DataHeader 1024*T_(C) IDS: Inter-Frame Data Spacing 3520*T_(C) T_(DS):Duration of Data Slot N_(DBM)*512*T_(C) = 24064*T_(C) T_(DP): Durationof Data Period N_(DS)*T_(DS) = 770048*T_(C)

The Data Preambles may be substantially shortened compared to the IEEE802.11ad Data Preambles based on the scheduled access architecture.

FIG. 27 is a diagram of an example of Data Period Structure. In theexample period 2700, the header data 2717 may be spread across two datablocks. The first slot 2710 may contain a preamble 2715, a header 2717and a payload 2719. Subsequent slots, for example slot 2 2720, maycontain data blocks. The final slot N 2730 may contain a data block, aGI, and inter-frame data spacing (IDS). Exemplary header fields arespecified in Table 17. The coding and modulation may be identical to theIEEE 802.11ad header coding and modulation.

FIG. 28 is a diagram of an example Data Preamble. The example shows theshortened preamble 2800, which contains only 7 Ga sequences used forAGC, CFO/SFO, and EoSTF. In an example, the preamble includes Ga 1 2810,Ga 2 2820, Ga3 2830, Ga 4 2840, and −Ga 7 2850, followed by CE block2860, GA 5 2870 and GA 6 2880. There may also be an additional 9 Gasequences that are intended to be used for channel estimation.

TABLE 17 Data Header Contents Size Field [Bits] Description MCS 5 Indexinto the currently used MCS table Identifies encoding scheme used toencode the message body. There may be multiple MCS tables for nodes withdifferent capabilities. This may be signaled when a node performsinitial association. Length 18  Additional 1 Indicates if the currentPPDU is PPDU immediately followed by another PPDU without a Preamble orInter-frame spacing. Set to ‘1’ in the first and subsequent PPDUs (ifany) that are aggregated. Set to ‘0’ in the last PPDU. As an example,the first PPDU may correspond to persistent traffic, while the secondPPDU may contain bursty traffic packets. The current design requires amaximum of 2 PPDUs per SI, however this value may be increased as analternative implementation option. Re- 2 or 4 Indicates whether thecurrent PPDU transmission is a new transmission or a HARQ Indicatorre-transmission. Multiple bits may be needed to signal if the currenttransmission corresponds to persistent or bursty traffic, at a minimum.FEC Indicator 1 or 2 Indicates if the long, short, or possibly otherspecific size LDPC code is used Power Control 2 Reserved 18 or 15 Beamtraining 5 Used to initiate and control beam info training Length: 3bits (Number of TRN-T/R subfields appended or requested) Beam TrackingRequest: 1 bit (1: beam tracking requested, 0: no beam trackingrequested) Packet Type: 1 bit (0: indicates either packet that has TRN-Rsubfields appended, or that sender is requesting TRN-R subfields beappended in a future response, 1: packet has TRN-T subfields appended.)RSSI 4 RSSI of last control message from this link Header Check 8 Ashort CRC sequence may be added to Sequence (HCS) check for decodingerrors. Total 64 

A data packet may span multiple Data Slots. In addition each packet maybe preceded by a preamble and a header and may end with a GI and IDS.These observations may lead to four possible configurations for a DataSlot in the default configuration of N_(cs)=5 and when no beam trainingis performed.

FIG. 29 is a diagram of an example of Various Data Slot Scenarios forN_(cs) equal to 5 and no beam refinement. In this example four possiblescenarios scenario 2910, scenario 2920, scenario 2930 and scenario 2940are depicted. In the example first scenario 2910, a data slot for thestart of packet that spans only one slot (i.e., the data slot is thefirst and last slot of packet) may start with a preamble of length TDPR,as required for each AGC, Timing Synchronization, and ChannelEstimation. The Preamble 2912 may be followed by a Header 2914 of lengthTDH, which may provide required parameters, shown in Table 17, in orderfor the node to be able to properly decode the data packet that follows.The Header may be followed by 34 Data Blocks 2915, each of which maycontain 448 coded bits followed by a 64 bit GI 2916. The GI 2916 may beused to update the CFO and other related timing parameters. After the GI2916, the 34 Data Blocks 2915 may be followed by an IDS 2918.

In the second example scenario 2920, a data slot for the start of apacket that spans multiple slots may start with the same Preamble field2922 and Header field 2924 as described above. The header field 2924 maybe followed by 41 Data Blocks 2925. Since the packet may continue intothe next Data Slot, there may be no final GI or IDS required.

In the third example scenario 2930, a data slot for the continuation ofa packet that spans additional slots (i.e., a slot that is neither thefirst or last slot of the packet) contains only 47 Data Blocks 2935,since the preamble and header were sent on the previous Data Slot. Inaddition, since the packet may continue into the next Data Slot, thereno final GI or IDS may be required.

In the fourth example scenario 2940, a data slot for the continuation ofa packet that ends in the current slot may start with only Data Blocks2945 as above, however, since the data packet ends in this slot, a GI2946 and IDS 2948 may both be required. There may be 40 Data Blocks 2945transmitted in this type of Data Slot.

When beam training is included in a packet, up to ceil{K*(4992/512)}data blocks may be lost to beam testing where K is the number of beams.For example when the number of control slots N_(cs) is greater than 5,then ceil{(22000/512)*(Ncs−5)}=ceil{(42.96875)*(Ncs−5)} data blocks maybe uniformly removed from the data region, reducing each slot by 1-2data blocks per slot per added control slot.

The following section considers a modified Low MCS Design at, forexample, 160 Mbps. The minimum required MAC-level data rate for the BHmay be targeted at 100 Mbps at a range of 350 meters. This may translateto a PHY-level data rate of 160 Mbps using a 62.5% MAC efficiency rate.The current 802.11ad MCS for single carrier (SC) provides PHY data ratesin the range of 385 Mbps to 4602 Mbps. These data rates are above therequired minimum for BH, however providing these rates may limit therange to less than the desired maximum range of 350 meters. Anotherpotential MCS already specified in IEEE 802.11ad is the CTRL-PHY MCS,which is more robust that any of the SC MCSs. Unfortunately, this MCSoption provides a PHY data rate of only 27.5 Mbps, which is well belowthe target BH data rate.

Table 18 lists the various exemplary parameters used throughout thebelow description.

TABLE 18 Low MCS Design Parameters Parameter Description Length Lengthof PSDU in octets R_(sc) ^(raw) Raw SC-PHY Data Rate R_(T) Target bitrate for Low MCS [160 Mbps] ρ Repetition factor with respect to N_(ρ) RLDPC Code Rate [½, ⅝, ¾, 13/16] R_(e) Effective Code Rate L_(CW) BaseLDPC codeword length [672] N_(CWLM) LDPC codeword length multiplierL_(FCW) Full LDPC codeword length [N_(CWLM)L_(CW)] L_(IW) Length ofInformation word F_(C) Chip Rate in MHz [1760] L_(DB) Length of DataBlock [512] L_(GI) Length of Guard Interval [64, 0] N_(ρ) Number ofInformation bits per codeword N_(DATA) _(—) _(PAD) Number of zero padbits appended to the end of the original PSDU N_(CW) Number of codewordsin one PSDU N_(BLKS) Number of Data Blocks N_(CBPB) Number of coded bitsper Data Block [L_(DB) − L_(GI)] N_(BLK) _(—) _(PAD) Number of zero padbits appended to the last Data Block

In order to determine the number of information bits required per datablock to provide a target bit rate, R_(T), of 160 Mbps, the raw SC-PHYdata rate may first be determined. Assuming Binary Phase Shift Keying(BPSK) modulation the raw SC-PHY bit rate may be found to be 1540 Mbpsthrough the following equation:

$\begin{matrix}{R_{sc}^{raw} = {\left( \frac{L_{DB} - L_{GI}}{L_{DB}} \right)F_{c}}} & {{Equation}\mspace{14mu}(7)}\end{matrix}$The SC-PHY information data rate, however, may need to take into accountthe fraction of information bits coming from the LDPC encoder, which maybe defined as:

$\begin{matrix}{R_{e} = \frac{L_{IW}}{L_{CW}}} & {{Equation}\mspace{14mu}(8)}\end{matrix}$

Using the two equations above the length of the information word perbase LDPC codeword length required, L_(IW), to support the targetPHY-level data rate, R_(T) may be determined as:

$\begin{matrix}\begin{matrix}{L_{IW} = \left\lceil \frac{R_{T}L_{CW}L_{DB}}{F_{c}\left( {L_{DB} - L_{GI}} \right)} \right\rceil} \\{= \left\lceil \frac{160*672*512}{1760\left( {512 - 64} \right)} \right\rceil} \\{= {70\mspace{14mu}{bits}}}\end{matrix} & {{Equation}\mspace{14mu}(9)}\end{matrix}$

With this in mind a modified MCS, referred to as “low MCS” is describedherein. This modified MCS may integrate seamlessly with the existingSC-PHY MCSs. An LDPC code rate of ½ may allow for

$\frac{L_{CW}}{2}$information bits per base LDPC codeword. Given that the length of theinformation bits, L_(IW), required for the modified low MCS may be lowerthan

$\frac{L_{CW}}{2},$along with the desire to integrate this modified MCS with the existingSC-PHY MCSs, an extension of the code word shortening and repetitionused in the IEEE 802.11ad standard may be used. The next sectiondescribes the modifications to the SC-PHY coding procedure required tosupport the modified low MCS. The coding procedure uses the existingMCSs and may use LPDC code word size of L_(FCW)=N_(CWLM)L_(CW), which istransparent to the coding procedure. The reason for making the LDPCcodeword size larger is explained below.

First, the total number of information bits per codeword may becalculated. If low MCS is used, this implies ρ>2 and is calculated as:

$\begin{matrix}{{N_{\rho} = \left\lceil \frac{R_{BT}L_{FCW}L_{DB}}{F_{C}\left( {L_{DB} - L_{GI}} \right)} \right\rceil},} & {{Equation}\mspace{14mu}(10)} \\{{\rho = {\frac{L_{FCW}R}{N_{\rho}}.{{Otherwis}e}}},} & {{Equation}\mspace{14mu}(11)} \\{N_{\rho} = \left\lceil \frac{L_{FCW}R}{\rho} \right\rceil} & {{Equation}\mspace{14mu}(12)}\end{matrix}$

Next, the number of data pad bits NDATA_PAD may be calculated using thenumber of LDPC codewords N_(CW):

$\begin{matrix}{{N_{CW} = \left\lceil \frac{8{Length}}{N_{\rho}} \right\rceil},} & {{Equation}\mspace{14mu}(13)} \\{N_{{DATA}\_{PAD}} = {{N_{CW}N_{\rho}} - {8{{Length}.}}}} & {{Equation}\mspace{14mu}(14)}\end{matrix}$

N_(CW) _(min) may be defined for BRP packets in IEEE 802.11ad. Thescrambled PHY service data unit (PSDU) may be concatenated with N_(DATA)_(_) _(PAD) zeros. They may be scrambled using the continuation of thescrambler sequence that scrambled the PSDU input bits. The procedure forconverting the scrambled PSDU data to LDPC codewords may depend on therepetition factor.

If ρ=1 (an 802.11ad MCS), the output stream of the scrambler may bebroken into blocks of N_(p) bits such that the mth data word is (b₁^((m)), b₂ ^((m)), . . . , b_(N) _(p) ^((m))), m≤N_(CW). To each dataword, n−k=L_(FCW)−N_(ρ) parity bits may be added to create the codewordc^((m))=(b₁ ^((m)), b₂ ^((m)), . . . b_(N) _(p) ^((m)), p₁ ^((m)), p₂^((m)), . . . , p_(n-k) ^((m))) such that Hc^((m)) ^(T) =0.

If ρ=2, which implies

$R = \frac{1}{2}$only with MCS1 as per IEEE 802.11ad, the data bits in each codeword (b₁^((m)), b₂ ^((m)), . . . b_(N) _(p) ^((m))) may be concatenated withN_(ρ) zeros to produce a sequence in length of 2N_(ρ), (b₁ ^((m)), b₂^((m)), . . . , b_(Nρ) ^((m)), 0₁, . . . , 0_(N) _(ρ) ). The LDPCcodeword c^((m))=(b₁ ^((m)), b₂ ^((m)), . . . , b_(N) _(ρ) ^((m)), 0₁, .. . , 0_(N) _(ρ) , p₁ ^((m)), p₂ ^((m)), . . . , p_(2N) _(ρ) ^((m))) maybe created by generating the parity bits p₁ ^((m)), p₂ ^((m)), . . . ,p_(2N) _(ρ) ^((m)) such that Hc^((m)) ^(T) =0, where H is the paritymatrix for rate ½ LDPC coding specified in IEEE. Bits N_(ρ)+1 through2N_(ρ) of the codeword c may be replaced with bits from the sequence b₁^((m)), b₂ ^((m)), . . . , b_(Nρ) ^((m)) XORed by a PN sequence that isgenerated from the LFSR used for data scrambling as defined in IEEE. TheLFSR may be initialized to the all ones vector and reinitialized to thesame vector after every codeword.

FIG. 30A is diagram of an example encoder for bit handling for low MCS.If ρ>2 this may indicate a low MCS condition. In this case, the outputstream of the scrambler may be broken into blocks 3010 of N_(ρ) bitssuch that the mth data word is (b₁ ^((m)), b₂ ^((m)), b_(N) _(ρ)^((m))), m≤N_(CW). For example a R value of R=½ may be used, but theremay a range of applicable values. Each data word may be concatenatedwith N_(z)=(L_(FCW)R−N_(ρ)) zeros 3020 to produce the following: (b₁^((m)), b₂ ^((m)), . . . b_(N) _(ρ) ^((m)), 0₁ ^((m)), 0₂ ^((m)), . . ., 0_(N) _(z) ^((m))). The LDPC codewords c^((m))=(b₁ ^((m)), b₂ ^((m)),. . . b_(Nρ) ^((m)), 0₁ ^((m)), 0₂ ^((m)), . . . 0_(N) _(z) ^((m)), p₁^((m)), p₂ ^((m)), . . . , p_(L) _(FCW) _((1-R)) ^((m))) may be createdby generating the parity bits 3030 (p₁ ^((m)), p₂ ^((m)), . . . , p_(L)_(FCW) _((1-R)) ^((m))) such that Hc^(T)=0, where H is the parity matrixfor rate R LDPC coding specified in IEEE 802.11ad. Bits 3042 N_(ρ)+1through 2N_(ρ) of codeword c may be replaced with bits from the sequence(b₁ ^((m)), b₂ ^((m)), . . . b_(Nρ) ^((m))) XORed by a PN sequence thatis generated from the LFSR used for data scrambling as defined in IEEE802.11ad. The LFSR may be initialized to the all ones vector andreinitialized to the same all ones vector after every codeword. Paritybits 3044 2N_(ρ)+1 through L_(FCW)R of codeword c may be replaced withbits from the sequence (p_(PR) ^((m)), p_(PR+1) ^((m)), . . . , p_(L)_(FCW) _((1-R)) ^((m))) XOR'ed by a PN sequence that is generated fromthe LFSR used for scrambling,) as defined in IEEE 802.11ad, wherePR=[(L_(FCW)(1−R))−(L_(FCW)R−2N_(ρ)+1)]. The LFSR may be initialized tothe all ones vector and reinitialized to the same vector after everycodeword.

The codewords may then be concatenated 3052 one after the other tocreate the coded bits stream c=(c₁, C₂, . . . , c_(L) _(FCW) _(N) _(Cw)). The number of symbol blocks, N_(BLKS), and the number of symbol blockpadding bits, N_(BLK) _(_) _(PAD), may be calculated as follows:

$\begin{matrix}{{N_{BLKS} = \left\lceil \frac{N_{CW}L_{FCW}}{N_{CBPB}} \right\rceil},{and}} & {{Equation}\mspace{14mu}(15)} \\{{N_{{BLK}\_{PAD}} = {{N_{BLKS}N_{CBPB}} - {N_{CW}L_{FCW}}}},} & {{Equation}\mspace{14mu}(16)}\end{matrix}$where N_(CBPB) is number of coded bits per data block. N_(CBPB) may betaken from IEEE 802.11ad.

The value for N_(BLKS) may be at most equal to the granted N_(BLKS),i.e., the number of data blocks contained the grant for the packet beingcoded as described above. The coded bit stream may be concatenated withN_(BLK) _(_) _(PAD) zeros 3054. They may be scrambled with acontinuation of the scrambler sequence that scrambled the PSDU data, andmodulated 3056 as per IEEE 802.11. The bit streams may then betransmitted through a channel.

FIG. 30B is diagram of an example decoder for bit handling for low MCS.The decoding process is effectively the reverse of the encoding processdescribed above. After demodulation, the demodulated sequence maycontain Information LLRs (for example, 3061 and 3062) and Parity LLRs(for example, 3064, 3066 and 3068). The Information LLRs may then bedescrambled, resulting in 3085. The resulting information bits 3085 maythen be combined with Zeroes 3090 and the parity bits. This combinationmay then be send to the LDPC decoder per codeword.

Longer LDPC codewords are now considered. As mentioned above, thebackhaul use case generally has more data available per packet than atypical IEEE 802.11ad use case. The performance generally improves ascodeword length increases. For these reasons, in examples longer LDPCcodewords may be supported for these backhaul use cases.

In a first example, LDPC codeword length and rate options may bebroadcast in beacon message 1 (no negotiation, system wide). In a secondoption, LDPC codeword length and rate options may be negotiated indiscovery message exchange (a.k.a. beacon message exchange). Nodecapabilities may be determined from its unique ID in the BRI. Thenetwork/existing node may decide on the LDPC length based oncapabilities of new and existing node and other things, and may includeinstructions in the beacon ACK. This may be done on a per link basis.LDPC word size may be indicated on a per data packet basis, either inthe control message exchange or in the data packet header. In a proposedexample, supported Forward error correction (FEC) methods may beincluded in the capabilities LUT. The attached nodes/network maydetermine the FEC capabilities from the signaled unique ID of the newnode (learn from BRI). All connected nodes may then know the capacitiesof their neighbors. The FEC method (e.g., LDPC codeword length) may besignaled in the data header per packet.

Considering HARQ and end-to-end latency, the mesh backhaul network maybe required to support very low latency packet delivery over at least 5hops through the mesh. The latency budget may require packets to bedelivered within 5 ms with high probability when there are no queuingdelays. The system may be designed such that failed packets may beretransmitted in the SI following the SI where the failure occurred. Forexample, if each SI is 0.5 mSec, the system may permit up to a total of5 retransmissions of the packet in route to the destination node.

HARQ may be used as a means to ensure this can be achieved withoutresorting to setting very low target packet error rates (PERs) on eachlink which could limit the ultimate achievable throughput. Suchretransmission may be identical copies to support chase combining or mayuse multiple redundancy versions.

In chase combining, either soft bits or soft symbols may be buffered forretransmission combining. When a first transmission fails, there-transmission may be combined (soft bit-wise or symbol-wise addition,possibly weighted for varying SNR between transmissions). In theAdditive White Gaussian Noise (AWGN) channel and a given target firsttransmission PER, the retransmission may enjoy nearly 3 dB of SNRimprovement for the purpose of estimating the PER on the retransmission.For example the LDPC codes may cause the 3 dB improvement results to bebetter PER than simple automatic repeat request (ARQ) retransmission. Anexample improvement in end-to-end packet delivery for line of sight(LOS) channels with minimal fading is estimated in FIG. 31 with andwithout HARQ.

The following section gives examples of simulation descriptions. In oneexample AWGN, the retransmit probability is nearly 3 dB better than the1st transmit probability for Chase combining, however 2.5 dB will beassumed to allow some margin for practical scenarios. If it is assumedthat channels vary slowly compared to the retransmit rate, which istypical for the BH case, then a conservative estimate for the SNRvariation for the retransmission should be limited to ˜+/−1.5 dB. Theoverall SNR improvement for the retransmission may then be calculated tobe about 1.9 dB.

Each link may use link adaptation techniques to achieve a target PER.For HARQ, the PER of a retransmission may then be computed byinterpolating a PER curve from the target PER point to the PER thatresults with 1.5 dB better SNR. In other words, the retransmit PER maybe estimated from the rate ½ LDPC curves by increasing the effective SNRby 1.5 dB relative to the SNR required to obtain the target 1sttransmission PER in the legend.

For ARQ, the statistical behavior for each transmission andretransmission may be considered to be independent and identicallydistributed (iid). With these assumptions ARQ lends itself to analyticalanalysis similar to a Bernoulli trial as follows. Given the iidcharacteristics as mentioned above, the probability of a packet beingsuccessfully delivered to the final destination node in exactly N_(SI)SIs using N_(H) hops and having failed N_(F) times along the way, may bewritten as follows:

$\begin{matrix}{{{{\overset{\sim}{P}}_{s}^{E\; 2E}\left( {N_{SI},N_{H},N_{F}} \right)} = {\left( P_{s} \right)^{N_{H}}\left( {1 - P_{S}} \right)^{N_{SI} - N_{H}}\left( \begin{pmatrix}N_{H} \\N_{F}\end{pmatrix} \right)}},} & {{Equation}\mspace{14mu}(17)}\end{matrix}$where {tilde over (P)}_(s) ^(E2E) (N_(SI),N_(H),N_(F)) is theprobability of a successful end-to-end packet delivery in exactly N_(SI)SIs, using N_(H) hops and having N_(F) failures along the way; N_(SI) isthe number of SIs used for the end-to-end transmission; N_(H) is thenumber of Hops used for the end-to-end transmission; N_(F) is the numberof single-hop failures for the end-to-end transmission, each requiring aretransmission; P_(S) is the probability of a successful single-hoptransmission; and

$\quad\left( \begin{pmatrix}n \\k\end{pmatrix} \right)$is the multiset coefficient, which represents the number of ways thatthe N_(F) failures could have occurred over the N_(H) hops, which isequal to:

$\frac{\left( {n + k - 1} \right)!}{{k!}{\left( {n - 1} \right)!}}.$

Furthermore, the probability of a packet being successfully delivered tothe final destination node within N_(SI) SIs using N_(H) hops and havingfailed N_(F) times along the way may be found by summing the aboveprobabilities for all successes. The summation starts from N_(H), whichis the minimum number of SIs required to deliver the packet to thedestination node, and ends at the maximum number of SIs chosen, N_(SI)^(max):

$\begin{matrix}{{P_{S}^{E\; 2E}\left( {N_{SI}^{\max},N_{H},N_{F}} \right)} = {\sum_{i = N_{H}}^{N_{SI}^{\max}}{{{\overset{\sim}{P}}_{s}^{E\; 2E}\left( {i,N_{H},N_{F}} \right)}.}}} & {{Equation}\mspace{14mu}(18)}\end{matrix}$Finally, the probability of the packet not being delivered by the N_(SI)^(max) SI may be written as:

$\begin{matrix}\begin{matrix}{{P_{F}^{E\; 2E}\left( {N_{SI}^{\max},N_{H},N_{F}} \right)} = \left\lbrack {1 - {P_{S}^{E\; 2E}\left( {N_{SI}^{\max},N_{H},N_{F}} \right)}} \right\rbrack} \\{= \left\lbrack {1 - {\sum_{i = N_{H}}^{N_{SI}^{\max}}{\left( P_{s} \right)^{N_{H}}\left( {1 -} \right.}}} \right.} \\{\left. {\left. P_{S} \right)^{i - N_{H}}\left( \begin{pmatrix}N_{H} \\N_{F}\end{pmatrix} \right)} \right\rbrack.}\end{matrix} & {{Equation}\mspace{14mu}(19)}\end{matrix}$A closed form expression for the probability of a successful end-to-endpacket delivery in the HARQ case has not yet been identified and sosimulations may be required. To get below 10⁻⁷ probability of a packetnot being received before 10 transmission time intervals (TTIs) in a 5hop route, ARQ may require a PER target ˜2%, but with HARQ a PER targetgreater than 20% may be supported. The scenario may be further extendedto include errors in both link adaptation and accounts explicitly forchannel quality variations between 1st and 2nd transmission.

The use of multiple redundancy versions may further improve HARQperformance, but for the backhaul, these gains may be expected to besmaller than for access links. In an example, multiple redundancyversions may be used.

FIG. 31 is diagram of an example Packet Delivery Time Probability withHARQ/ARQ. The graph 3100 depicts the probability of a packet notdelivered in N TTIs for different PER and 5 hops.

Variable-length preambles for Control Period messages are relevant forbackhaul networks due to the static nature of the nodes, and due torelatively high periodicity of message exchange between the nodes. Thesetwo conditions imply that the channel between the mmW backhaul nodesremains fairly static between successive message exchanges, and ashorter preamble would suffice for the AGC settling, channel estimation,and other related purposes. Although this variable-length preamble ideais described here in the context of backhaul mesh nodes, it may beapplied whenever the change in channel conditions between thetransmitting and receiving nodes is less than a particular threshold.This procedure may allow node pairs to determine the best preamble size,based on local channel conditions. In addition it may reduce the controloverhead due to the preamble significantly, which is a direct overheadfor each PHY layer frame transmission.

Determining the optimal preamble size so as not to impact performance ofAGC (channel estimation etc.), and at the same time reducing thepreamble size taking into account the static nature of the backhaullinks may significantly improve the overall good-put of the system.Further, taking into account when the last data transmission hasoccurred may further improve the overall good-put of the system.

FIG. 32A is a diagram of an example of a variable-length preamble. In anexample variable-length preamble, the node may have a-priori knowledgeof preamble lengths. In this example, when the requirements of the timedifference between successive packet transmissions of the same pair ofnodes are satisfied, the transmitter may implicitly switch to a shorterlength preamble 3220 for the second and subsequent packet N, as long asthe duration between successive transmissions is less than somepredefined value. In an example a first packet may contain Preamble 13210 and Information 3219 and a subsequent packet may contain Preamble 23220 and Information 3225. Further, later packets may follow, through apacket which may contain Preamble N 3230 and Information 3235. In anexample, the transmitter may switch to a shorter preamble for Preamble 23220 and Preamble N 3230, if the duration is less than the predefinedvalue. This predefined value may be signaled as part of initialconfiguration or can be loaded from memory. The transmitter may choosethe appropriate preamble length based on the duration since the lastsuccessful transmission to the same receiving node. In a furtherexample, signals regarding the initial preamble length may be receivedfrom a central node. In a further example, the preamble length may bebased on the content of the transmission. Therefore, there may bemultiple possible preamble lengths and the transmitter may choose theappropriate one depending on one or more of several factors.

The receiver may also determine the preamble size in the nexttransmission from the same node in a similar manner. In an example, thepacket is correctly received by the receiver, but an acknowledgementsent in response is not received at the first node. The first node mayuse a longer preamble if a short preamble timer has elapsed) in the nexttransmission because the first node failed to receive theacknowledgement. Nevertheless, the second node may still expect a shortpreamble. In this circumstance, the second node may simply ignore theremaining part of the preamble. If the acknowledgement is received atthe first node, then the first node may continue to use the shorterpreamble. In a further example, the transmitter may also know theappropriate preamble length based upon the estimated channel conditions,and adjust the preamble length accordingly. In a further example, thetransmitter may adjust the preamble length based on local channelconditions.

FIG. 32B is a diagram of another example of a variable-length preamble.In this second example, the explicit signaling of the preamble lengthmay be at the start of the preamble itself. Accordingly, the preamblemay have two parts the first part of the preamble 3242 may indicate thelength of the second part 3244. Information 3245 may follow the secondpart of the preamble 3244. The transmitter may use one out of N possiblesequences for the first part of the preamble. The different sequencescorrespond to N different lengths for the second part of the preamble.The receiver may then determine the preamble length by cross-correlatingthe first part of the preamble against all N possible sequences.Explicit signaling of the preamble length may make it possible for thetransmitter to adapt the preamble length according to local channelconditions. In a further example, the transmitter may also adapt thepreamble length to estimated channel conditions. It may also bedesirable for the codes used to determine the preamble length to havegood auto correlation properties (low non-zero lag peaks) and low crosscorrelation peaks between members of the possible sequences.

In the third example, the requested preamble length may be signaled by amesh node to its peer neighboring node. This signaling may either inabsolute terms or relative to the preamble length used for the previoustransmission from the peer node. This field may be included in thePhysical layer (PHY) or Physical Layer Convergence Protocol (PLCP)Header. For example, one example may reserve two bits in the PHY/PLCPHeader to indicate requested change in preamble size. Here 00 mayrepresent no change, 01 may represent request for longer preamble and 10may represent request for shorter preamble size. Accordingly, Node 1 mayset the value of this field to 10 to request Node 2 to reduce thepreamble length in its next transmission to Node 1, if time limitationsare satisfied.

Conversely, if Node 1 fails to correctly decode the previoustransmission from Node 2 due to insufficient preamble size, resulting inincorrect channel estimation or failure of AGC to settle, it may requestlonger preamble in the next transmission from Node 2 by sending aNull-Data frame with the Preamble Length field in the PHY/PLCP Headerset to 01. This may provide a closed-loop mechanism for the nodes toadjust the preamble size according local channel conditions. If theduration between successive data transmissions to the same receivingnode is larger than a particular limit, then the transmitting node maydefault to a larger preamble size, irrespective of the request from thereceiving node in the previous transmission. In another variation, therequesting node may include the requested preamble length in absoluteterms, but this may need a larger field in the Header depending on thenumber of active preamble sizes.

In example disclosed herein, modified complementary Golay codes areused. The Golay sequences and complementary pairs used in the preambleof the backhaul system may be similar to the ones used in IEEE 802.11adand may be composed of 128-chip long sequences. Further the code mayhave a recursive construction. However, the system may support the useof multiple such Golay building blocks and the exact codes used may beselected to have good properties relative to IEEE 802.11ad and to eachother. The Golay sequences used in the backhaul system may be designedto have low correlation at any lag to the Ga and Gb sequences of802.11ad, good auto correlation properties (low non-zero lag peaks), andlow cross correlation peaks between members of the possible Golaysequences.

During discovery, each node may be given an index that points to one ormore sets of Golay sequences (e.g., a Ga and Gb Golay complementary pair(GCP) of 128 chips). The index may be node or link specific. There are8-16 different sets of GCPs available for use. During discovery, the newnode may be told which Golay index to use to determine which sequencesit will use to transmit.

There are 2^(M)M! Golay codes (with GCPs) that can be generated fromrecursive or direct construction For M=7, that is just over half amillion and within reach of exhaustive search for codes with lowcorrelation to the IEEE 802.11ad 128 chip codes.

FIG. 33 is a diagram of an example distribution of peak correlations tothe 802.11ad Golay codes. Distribution 3300 shows a peak valuedistribution of a set of all of the Golay codes of length 128 that canbe constructed from the Direct construction method. A set of codes withlow cross correlations between IEEE 802.11ad Ga and Gb may be chosen ina further example. Of these codes, 1140 have a peak cross correlation ofless than 28 (the minimum correlation values in 24, but the set issmall).

From this set, a smaller set of Ga sequences may be found that have lownon-zero lag auto correlation peaks so that they may make for goodsequences for packet detection without use of the complementary pair.For example, a set of codes is desired such that each of the codes has amaximum peak no more than 5 greater than the sequence with the minimummaximum peak. This may reduce the set to about 190 sequences. While thisset is drastically reduced from the original half million, finding agood set of codes, for example 8-16 codes, with good cross correlationproperties may not be required as a random search produces reasonablylow cross correlation sets. The delays and weights for an exemplary setof 8 GCPs with peak cross correlation of 28 or less is shown in Table 19and Table 20. Another set of 16 GCPs with peak cross correlation of 34or less is shown in Table 21 and Table 22. Better search methods may beused to further refine this set but may not be required as the initialselection of Golay codes only show that ‘good enough’ codes may indeedbe found.

After the initial setting of the Golay index, the node may bereconfigured to use a different Golay index via higher layer signaling.The selection of codes is meant to minimize the effects of large crosscorrections that could impact packet detection and timing estimates aswell as channel estimation due to interfering sequences from IEEE802.11ad networks, from other nodes within the backhaul network, or fromnodes in other backhaul.

TABLE 19 Example Set of Delays for the Generation of 8 GCP with MutualXcorr <= 28 D1 D2 D3 D4 D5 D6 D7 D8 1 1 4 4 1 16 1 1 64 64 64 64 4 8 2 88 8 1 1 16 4 16 16 2 2 2 2 64 64 8 4 16 16 8 8 2 32 64 2 4 4 32 32 32 132 64 32 32 16 16 8 2 4 32

TABLE 20 Example Set of Weights for the Generation of 8 GCP with MutualXcorr <= 28 W1 W2 W3 W4 W5 W6 W7 W8 1 1 −1 −1 1 −1 −1 1 1 1 −1 −1 −1 1 1−1 −1 −1 −1 −1 1 1 1 −1 −1 −1 −1 −1 −1 −1 1 −1 −1 −1 −1 −1 1 −1 1 −1 −1−1 −1 −1 1 1 1 1 1 −1 −1 1 −1 −1 −1 1

TABLE 21 Example Set of Delays for the Generation of 16 GCP with MutualXcorr <= 34 D D D D D D D D D D D D D D D D 1 2 3 4 5 6 7 8 9 10 11 1213 14 15 16 1 1 16 2 16 1 1 1 1 4 1 1 1 1 16 16 2 64 8 64 8 64 2 64 1664 4 64 8 16 8 8 64 8 1 1 1 2 4 16 4 1 16 8 16 2 1 4 8 2 64 32 64 32 642 64 2 64 2 4 32 64 64 16 16 32 16 32 16 32 8 2 8 2 16 2 4 32 32 4 4 4 84 8 8 32 8 32 32 4 64 8 4 1 32 32 2 4 2 4 16 4 32 16 8 32 32 64 2 2

TABLE 22 Example Set of Weights for the Generation of 16 GCP with MutualXcorr <= 34 W W W W W W W W W W W W W W W W 1 2 3 4 5 6 7 8 9 10 11 1213 14 15 16 1 −1 −1 1 −1 1 1 −1 −1 −1 1 1 1 −1 −1 −1 1 1 −1 −1 −1 −1 −11 −1 −1 −1 −1 −1 1 −1 1 1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −1 1 −1 −1 −1 −1 −1−1 −1 1 −1 −1 1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 1 −1 −1 −1 1 −1 −1 1 −1 11 −1 1 −1 −1 1 −1 −1 −1 −1 1 1 −1 1 1 1 −1 1 1 −1 1 −1 −1 1 1 −1 −1 −1−1 1 1 1 1 1 1

The 64 chip code used in the GI period may be derived from the Golaycode indicator as well. A similar procedure may be used to findappropriate sets of Ga-64 can be used. Power control procedures may alsobe updated in a further example.

During the creation of each of the 224 bit-codewords, parity bits may bepunctured from the center of the LDPC parity bit field plus some offset.PO_(max) represents the maximum offset, or PO, relative to the center ofthe parity bit field of the LDPC codeword that can be supported. Inorder to gain insight into how the particular choice of PO affects theperformance a number of simulations were configured where PO was sweptover a given range. For reference a simulation was also run where PO waskept constant. The configurations of the various example simulationswere as shown in Table 23.

TABLE 23 PO Sweep Test Configurations Simulation Code Rate Message SizeNumber [R] [Bits] PO values 0 ½ 46 PO_(max) 1 ½ 46 {−PO_(max): PO_(max)}2 ⅝ 46 {−PO_(max): PO_(max)} 3 ¾ 64 {−PO_(max): PO_(max)} Note:Simulation 3 is the same as the SC-PHY header used on 802.11ad

FIG. 34 is a diagram of an example result from a simulation. Result 3400may show results with a shortened code and repetition, a rate of 0.5LDPC, 46 msgBits and 5000 Num blocks. Result 3400 may further show areference example of multiple runs of the same PO. Result 3400 may alsoshow there may be less of a variation in performance of simulation 0compared to simulations 1, 2 and 3. This observation validates theconclusions that will be drawn from simulations 1, 2 and 3.

FIG. 35 is a diagram of an example result from another simulation.Result 3500 may show results with a shortened code and repetition, asweep of POs, a rate of 0.5 LDPC, 46 msgBits and 5000 Num blocks. Result3500 shows the performance spread of simulation 1 may be about ½ dB at1% block error rate (BLER). Result 3500 may also show R of ½, a messagesize of 46 and PO=−POmax: −10.

FIG. 36 is a diagram of another example result from another simulation.Result 3600 of simulation 1 highlights that −PO_(max) is the best choicein the typical sense. Result 3600 may show BER at −4 dB, −3 dB SNRversus PO and message bit=46 rate=0.5. Result 3600 may also show BLERplotted versus PO at two different SNRs.

FIG. 37 is a diagram of an example result yet another simulation. Result3700 may show results with a shortened code and repetition, a sweep ofPOs, a rate of 0.625 LDPC, 46 msgBits and 5000 Num blocks. Result 3700of simulation 2 shows a similar performance spread as in simulation 1.Result 3700 may also show R of ⅝, a message size of 46 and PO=−POmax:−10.

FIG. 38 is a diagram of an example of another result from anothersimulation. Result 3800 of simulation 2 shows that −PO_(max) may be thebest choice in the typical sense. Result 3800 may show BER at −4 dB, −3dB SNR versus PO and message bit=46 rate=0.625. Result 3800 may alsoshow BLER plotted versus PO at two different SNRs.

FIG. 39 is a diagram of an example result from yet another simulation.Result 3900 may show results with a shortened code and repetition, asweep of POs, a rate of 0.75 LDPC, 64 msgBits and 10,000 Num blocks.Result 3900 of simulation 3 shows a similar performance spread as insimulation 1. Result 3900 may also show R of ¾, a message size of 64 andPO=−POmax: −10.

FIG. 40 is a diagram of another example result from an additionalsimulation. Result 4000 of simulation 3 may also show that −PO_(max) isthe best choice in the typical sense. Result 4000 may also show BER at−4 dB, −3 dB SNR versus PO and message bit=64 rate=0.75. Result 4000 mayalso show BLER plotted versus PO at two different SNRs. Note that thissimulation may be configured similar to the SC-PHY header in IEEE802.11ad. More importantly, IEEE 802.11ad uses −PO_(max) which isactually the worst PO that could be selected according to thesimulation.

FIG. 41 is a diagram of an example comparison of the results ofsimulations. Result 4100 compares simulation 2 with simulation 3. Result4100 may show results with a shortened code and repetition, a sweep ofLDPC coderates, 64 msgBits, 10,000 Num blocks and an efficiency rate pereach method for 2 CWs of 0.2857. Further, result 4100 may show themodified method performs better because it can utilize the lower coderate. Further, the modified method may be flexible enough to take alarge range of word sizes.

The IEEE 802.11ad method uses the ¾ rate code, possibly to minimize zeropadding. This strategy, however, may increase the overall code rates andthus may lead to lower performance depending on the message payload. Thebest choice of R is not clear for the general case and therefore the Ris left as a system parameter so that best performance can be obtainedfor any payload size.

In examples, the low MCS was integrated with the existing MCSs in theBWT link level (LL) test bench (TB). Simulations were run to verify theperformance. In order to use the existing SC-PHY header (or smallmodification of it), the performance of the modified low MCS, althoughexpected to be better than MCS1, may still leave ˜2 dB margin withrespect to the header performance. With this in mind three separateexample performance simulations were run: SC-PHY header (the 802.11adversion is used, but we note the modified version will have performanceat least as good as the 802.11ad version), MCS1, and Low MCS.

The simulation parameters were as follows: lx data sampling, AWGNchannel, ideal SoP/EoSTF, no radio impairments, realistic CHEST and datadetection, and PSDU length. While these simulations are idealistic, therelative performance of the different transmissions should not be overlydistorted by these assumptions.

FIG. 42 is a diagram of an example comparison of multiple simulations.The following may be observed in result 4200: Low MCS performs at about2 dB better than MCS1 at 1% PER (this was expected due the lowereffective coding rate), and the header performance may still be betterthan low MCS by ˜4 dB at 1% PER. This may meet the ˜2 dB margin, whichmay allow for the original SC-PHY header to be used unchanged. Result4200 may also show one times sampling, an ideal SoP/EoSTF, realisticCHEST and no radio impairments.

The IEEE 802.11ad standard lists the receiver sensitivity for all SC-PHYMCSs. The receiver sensitivity for the modified low MCS may becalculated using the same performance criteria and degradationassumptions. The performance criterion is stated as “The PER shall beless than 1% for a PSDU length of 4096 octets using the input leveldefined at the antenna port.” The simulation specification also assumesa 5 dB example loss and a 10 dB noise factor. However, using the MCS1,the criteria may be compared to the performance obtained with thesimulation parameters specified as above. The specified receiversensitivity, S_p, for MCS1 is started at −68 dBm. Next, using a 1.76 GHzBW, the thermal noise power is calculated asN _(p)=10 log(KTB)=−81.5 dBm.  Equation (20)Therefore the required SNR at the antenna port to be supported is:SNR_(AP) =S _(p) −N _(p)=−68+81.5=13.5 dB.  Equation (21)Next, assuming 15 dB of degradation, as specified above, the SNR atwhich the 1% PER requirement refers to is −1.5 dB:SNR_(R)=SNR_(AP)−SNR_(D)=−1.5 dB.  Equation (22)Result 4200 shows the 1% PER is at about −1.5 dB for MCS1 matching thespecification. It may be assumed the operating environment used in thesimulations is accurate. As shown in Result 4200, the modified low MCSmay perform ˜2 dB better so that the SNR_(R) at 1% PER is about −3.5 dBandSNR_(AP)=SNR_(R)+SNR_(D)=11.5 dB.  Equation (23)The receive sensitivity for the modified low MCS may now be calculatedas:S _(P)=SNR_(AP) +N _(p)=11.5−81.5=−70 dBm.  Equation (24)

To achieve an example range of 350 m with the modified low MCS, areceived power of −70 dBm at the antenna port (after any array gain andantenna losses) is required. There are multiple antenna configurationsthat may be used to achieve this. For the purposes of this example, thefollowing assumptions are made: the same number of antenna elements areused for Tx and Rx; the elements are printed patch antennas with gain of5.5 dBi; Equivalent Isotropically Radiated Power (EIRP) limited FederalCommunications Commission (FFC) limit of 40 dBm; total Tx power is lessthan 10 dBm (European Union (EU) and other regional limits); molecularoxygen absorption is equal to 13 dB/km; rainfall losses is equal to 10dB/Km (25 mm/Hr); and 3 dB a loss in Rx antenna (e.g., feed network).

With these assumptions, the low MCS link may be closed at 350 m with 100Tx and Rx antenna elements, total Tx power equal to 10 dBm, EIRP equalto 35.5 dBm, Half Power Beamwidth (HPBW) equal to 11.5 deg (for square10×10 arrangement). While these arrays are seemingly large, thefollowing observations may be made. The 10 dBm Tx power limit is onlyfor 60 GHz and outside of the US. The FCC permits higher power, and theEIPR limit is higher outside of the US and outside of 60 GHz. Techniquesto scale antenna to thousands of elements may be feasible with massproduction techniques. Most links may not need to support 350 m; 150 mis more typical.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, UE, terminal, base station, RNC, or any host computer.

What is claimed is:
 1. A method implemented in a mesh node for use inmesh operations, the method comprising: receiving, by the mesh node, asignal including a preamble, wherein the preamble includes a first Golaysequence that is different from a second Golay sequence, wherein thesecond Golay sequence is an initial Golay sequence; adjusting, by themesh node, the preamble based on the received first Golay sequence; andsending, by the mesh node, transmissions using the adjusted preamble toa neighboring node.
 2. The method of claim 1, wherein the signalincluding the preamble is received from a central node.
 3. The method ofclaim 1, wherein the first Golay sequence included in the preamble isbased on content of a data payload in a received transmission.
 4. Themethod of claim 1, further comprising: sending, by the mesh node,transmissions using the adjusted preamble to a plurality of neighboringnodes.
 5. The method of claim 1, further comprising: adjusting, by themesh node, a preamble based on estimated channel conditions for at leastone neighboring node.
 6. The method of claim 1, further comprising:sending, by the mesh node, further transmissions using the adjustedpreamble based on receiving an acknowledgement or using a preamblelonger than the adjusted preamble based failing to receive anacknowledgement.